2023 ACVIM Forum Research Abstract Program

Colorado State University, Fort Collins, CO, USA

Background: Quantitative assessment of mitral regurgitation (MR) severity has become increasingly important as surgical and catheter-based therapies for MR reduction become available.

Hypothesis/Objectives: Obtain quantitative measures of MR severity across stages of degenerative mitral valve disease (DMVD) and evaluate agreement between two methods.

Animals: 51 client-owned dogs stratified across three stages of DMVD (ACVIM B1, B2, and C).

Methods: Regurgitant volume (RVol) and fraction (RF) were measured on echocardiograms prospectively acquired by a single cardiologist by using Simpson's method of discs (volumetric) and proximal isovelocity surface area (PISA) methods. RVol and RF were compared by both methods across disease stage (Kruskall–Wallis, Conover). Agreement between methods over the range of MR severity was determined by Bland-Altman analyses. Intra- and inter-observer measurement variability assessments were made via intraclass correlation coefficients (ICC).

Results: RVol was different (P < 0.0001) across stage by both volumetric (B1—0.09 mL/kg; B2—1.49 mL/kg; C—2.72 mL/kg) and PISA (B1—0.39 mL/Kg; B2—1.67 mL/kg; C—3.1 mL/kg) methods. Similarly, RF was different (P < 0.0001) across stage by both volumetric (B1—13.6%, B2—55.6%, C—67.2%) and PISA (B1—34.3%, B2—58.8%, C—75.2%) methods. Bias between volumetric and PISA for RVol (0.24 mL/kg) and RF (13.7%) was biologically acceptable; however, the limits of agreement were wide. Proportional bias between methods was not present for RVol (P = 0.79) or RF (P = 0.53). Aside from PISA RF, intra- and inter-observer variability assessments showed ICC greater than 0.81.

Conclusions and Clinical Importance: Measurement of RVol and RF provide relevant information on MR severity across ACVIM stages of DMVD. Volumetric and PISA methods are not interchangeable.

¹Royal Veterinary College, London, England, UK; ²Senior Clinician in Cardiology, Langford Vets, UK; ³Veterinary Cardiologist, Ospedale Veterinario San Francesco, Italy; ⁴Professor of Veterinary Cardiology, Royal Veterinary College, London, England, UK

Background: Short-axis left atrial diameter indexed to the aorta (LA/Ao), usually measured at end-systole (LA/Aomax), might be easier to measure at end-diastole (LA/Aomin) without sacrificing prognostic value.

Hypothesis: LA/Aomin would be more repeatable than LA/Aomax and be an independent predictor of survival in cats with hypertrophic cardiomyopathy (HCM).

Animals: 247 client-owned cats (81 healthy cats, 118 HCM stage B cats and 48 HCM stage C cats).

Methods: Patient records were retrospectively reviewed, and LA/Aomax and LA/Aomin measured by two investigators. Data presented as mean (95% CI).

Results: LA/Aomin reference interval for healthy cats was 0.84 (90% CI 0.80–0.87) to 1.28 (90%CI 1.25–1.32). Compared to LA/Aomax, LA/Aomin showed a higher inter-operator ICC (0.99 [0.98–1.00] versus 0.91 [0.80–0.97]), lower inter-operator CV (6.6% versus 10.6%) and less bias (−0.01 [−0.18–0.16] versus −0.13 [−0.43–0.18]). The aortic valve was visible 64% less frequently for LA/Aomax than LA/Aomin (χ² = 14.9, P < 0.001). In receiver operating characteristics curve analysis LA/Aomin differentiated stage C from stage B cats with an area under the curve (AUC) of 0.95 (0.92–0.98), similar to LA/Aomax (AUC 0.94 [0.90–0.98]). Kaplan-Meier analysis showed an LA/Aomin >1.9 (upper quartile) was associated with increased all-cause mortality (P < 0.001), with no difference between other quartiles (P > 0.4). The univariable Cox's proportional hazard ratio for LA/Aomin >1.9 was 7.5 (3.76–16.3). Multivariable analysis identified LA/Aomin >1.9, symptomatic status and left ventricular systolic function as independent predictors of survival.

Conclusions and Clinical Importance: LA/Aomin demonstrated higher repeatability compared to LA/Aomax and was an independent predictor of survival in cats with HCM.

¹Atlantic Veterinary College, University of Prince Edward Island, Prince Edward Island, Canada; ²Professor, Companion Animals, Atlantic Veterinary College, University of Prince Edward Island, Prince Edward Island, Canada; ⁴Cardiologist, VCA West Los Angeles Animal Hospital, Los Angeles, CA, USA

Background: Clinically, dogs are screened for subaortic stenosis (SAS) using 2-D and Doppler echocardiography. Distinguishing between mild SAS and unaffected can be difficult, and a more precise evaluation of the left ventricular outflow tract (LVOT) is desirable.

Hypothesis/Objectives: To determine the step-up in Doppler-derived peak velocity at different sites of the LVOT and ascending aorta, investigate associated factors, and determine the aortic orifice area using 2-D and 3-D echocardiography in dogs.

Animals: Sixty-nine healthy, privately owned dogs.

Methods: Prospective study evaluating 2-D, spectral Doppler, and 3-D echocardiographic indices of the LVOT and aorta.

Results: Obtaining 3-D images and performing LVOT planimetry was feasible in all dogs (body weight: 4.8–56.6 kg). The mean (range) total step-up in velocity from LVOT to ascending aorta was 105 cm/s (65–168 cm/s) and 83 cm/s (34–128 cm/s) from subcostal and left apical (Lap) views, respectively. Subcostal-derived peak LVOT velocity was higher than Lap (P < 0.001), and peak velocities derived from both imaging planes were greater after behavioral stimulation (P < 0.001). Heart rate, left ventricular volume, and 3-D echocardiography-derived aortic valve (AoV) area were significantly associated with LVOT velocity. The 3-D planimetric AoV area was greater than the 2-D AoV annulus diameter-derived area (P < 0.001). The continuity equation underestimated 2-D and 3-D measures of LVOT area.

Conclusions and Clinical Importance: These results quantify the expected step-up in LVOT velocity and identify associated factors in apparently normal dogs. This information can be used for improving the accuracy of echocardiography in assessing dogs for SAS.

¹Royal Veterinary College, London, England, UK; ²Undergraduate Student, Royal Veterinary College, London, England, UK; ³Senior Clinical Training Scholar in Veterinary Cardiology, Royal Veterinary College, London, England, UK; ⁴Professor of Small Animal Surgery, Royal Veterinary College, London, England, UK

Background: Dogs that undergo mitral valve repair (MVR) for degenerative mitral valve disease (DMVD) frequently have degenerative tricuspid valve disease (DTVD). The significance of DTVD in these dogs has not been studied, therefore it is currently challenging to know if concurrent or subsequent tricuspid valve repair should be considered.

Hypothesis: DTVD is common in dogs that have undergone MVR but right-sided congestive heart failure (R-CHF) because of DTVD is rare.

Animals: 83 dogs that had MVR surgery.

Methods: Retrospective study. Case history and echocardiographic reports of dogs that had undergone MVR were reviewed. Dogs with severe pulmonary hypertension (PHT) were excluded from outcome analysis.

Results: Study dogs represented 26 different breeds; median age was 9 years (range 5–14 years) with a mean follow-up time of 1.6 years. Prior to MVR 27% of dogs had moderate-severe tricuspid regurgitation (TR) and there was no difference in the proportion of dogs with moderate-severe TR at each follow-up (1, 6 months, 1, 2 and 3 years, P = 0.25). At date of last follow-up 59/83 (71%) dogs had tricuspid regurgitation documented. One dog developed severe PHT and R-CHF 6 mo post-MVR. Severe DTVD (without PHT) occurred in 2/83 (2.4%) dogs, with onset of R-CHF at 1 and 4 years post-MVR. The former dog was alive at last follow-up (3 years) and the latter dog was euthanized 4.5 years post-MVR due to R-CHF.

Conclusions and Clinical Importance: Progression of DTVD to R-CHF is rare and therefore simultaneous tricuspid valve repair in dogs undergoing MVR is not justified and would likely present an additional unnecessary risk.

¹Angell Animal Medical Center; ²Cardiologist, Cardiology, Angell Animal Medical Center; ³Internist, Internal Medicine, Angell Animal Medical Center, Boston, MA, USA; ⁴Heart of Veterinary Cardiology

Background: The pro-arrhythmic effects of thyroid hormones are well-documented in people. Multiple ECG abnormalities have been reported in hyperthyroid cats. Few studies have evaluated echocardiographic and cardiac biomarker parameters pre- versus post-radioiodine treatment for feline hyperthyroidism. It is unknown whether ECG abnormalities improve post-radioiodine therapy in cats.

Objectives: Evaluate 5-minute ECGs in hyperthyroid cats undergoing I-131. The hypothesis was that radioiodine treatment would result in improvement of supraventricular and/or ventricular arrhythmias. Additional objectives were to characterize ECG, echocardiographic, and N-terminal pro-B-type natriuretic peptide (NT-proBNP) changes over time.

Animals: Client-owned cats undergoing I-131; 32 cats were initially eligible for inclusion. Six cats were excluded, 26 cats were enrolled. One cat did not complete the final evaluation due to euthanasia for non-cardiac reasons.

Methods: Single-center, prospective study completed June 2021–January 2023. Initial evaluation performed immediately prior to I-131: physical exam, blood pressure, echocardiogram, NT-proBNP, thyroid level (T4), and 5-min 6-lead ECG. Recheck blood pressure, ECG, T4, and NT-proBNP were performed 4–6 weeks later. Final evaluation 4–6 months post radioiodine therapy repeated all initial diagnostics.

Results: Preliminary analyses revealed a reduction in T4 following I-131 was associated with a statistically significant reduction in left atrial size (2-D left atrial to aortic root ratio), left ventricular free wall thickness, left ventricular fractional shortening, NT-proBNP, weight, and average heart rate. There was a significant reduction in the number of patients with arrhythmias.

Conclusions: Prospective studies utilizing 24-hour Holter or telemetry monitoring are needed to further characterize arrhythmias in hyperthyroid cats undergoing radioiodine therapy.

¹Colorado State University, Fort Collins, CO, USA; ²University of Georgia, Athens, GA, USA

Background: Differentiating cardiogenic versus noncardiogenic causes of respiratory signs can be challenging when echocardiography is unavailable. Radiographic vertebral left atrial size (VLAS) and vertebral heart size (VHS) have been shown to predict echocardiographic left heart size, with VLAS specifically estimating left atrial size.

Hypothesis/Objectives: Compare the diagnostic accuracy of VLAS and VHS to predict 12 left-sided congestive heart failure (CHF) in dogs presenting with respiratory signs.

Animals: One hundred and fourteen dogs with respiratory signs and radiographic pulmonary abnormalities.

Methods: Retrospective cross-sectional study. Dogs had to have an echocardiogram and thoracic radiographs obtained within 24-h. Diagnosis of CHF was confirmed based on the presence of respiratory signs, cardiac disease, LA enlargement, and cardiogenic pulmonary edema.

Results: Fifty-seven dogs had CHF—yes, and 57 had CHF—no. Compared to VHS (area under the curve [AUC] 0.85, 95% CI 0.77–0.91), VLAS was a significantly (P = 0.03) more accurate predictor of CHF (AUC, 0.92, 95% CI 0.85–0.96). Optimal cutoff for VLAS was >2.3 vertebrae (sensitivity 93.0%, specificity 82.5%). Compared to murmur grade (P = 0.40) and VHS (P = 0.11), only VLAS (P < 0.0001) was independently associated with CHF. Increased VHS (54%) was significantly (P = 0.007) more common than increased VLAS (24%) in dogs with CHF—no. Results were similar in a subpopulation of older and smaller dogs.

¹University of Wisconsin, Madison, WI, USA; ²Cardiology Faculty Member, Medical Sciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI, USA; ³Cardiologist, MedVet Medical and Cancer Centers for Pets; ⁴Cardiologist, Veterinary Specialty Services

Background: Time- and dose-dependent side effects of amiodarone have not been described in cats.

Hypothesis/Objectives: Report laboratory findings, adverse events, and clinical outcome in cats receiving amiodarone therapy.

Animals: Twenty-seven client-owned cats treated with amiodarone.

Methods: Medical records were reviewed for signalment, arrhythmia diagnosis, presence of structural heart disease and congestive heart failure at presentation, amiodarone dose, and adverse events. The median ALT, ALP, and T4 values were compared before and after short-term treatment (0–3 months) and long-term treatment (>6 months).

Results: Amiodarone was most commonly prescribed for ventricular arrhythmias with a median dose of 50 mg/cat/day (range 25–50 mg/cat/day). Most cats had cardiomyopathic disease (26/27; 96%) and many were in congestive heart failure (17/27; 63%) at presentation. Cats received amiodarone for a median of 141 days (range 3–1543 days). The ALT significantly decreased following short-term treatment (n = 19; P = 0.01), but there was no significant difference in ALP (n = 19; P = 0.94) and T4 (n = 4; P = 0.25). There was no significant difference in ALT (n = 9; P = 0.65) and ALP (n = 10; P = 0.87) in cats treated with amiodarone for more than 6 months. Ten cats (37%) had at least one episode of hyporexia or vomiting while receiving amiodarone.

Conclusions and Clinical Importance: In cats, amiodarone was used primarily for ventricular arrhythmias and appeared to be generally well tolerated. Transient gastrointestinal signs were reported in cats receiving amiodarone.

¹North Carolina State University, Raleigh, NC, USA; ²Adjunct Professor of Cardiology, Department of Clinical Sciences, North Carolina State University, Raleigh, NC, USA; ³Assistant Professor of Cardiology, Department of Clinical Sciences, North Carolina State University, Raleigh, NC, USA; ⁴Professor of Cardiology, Department of Clinical Sciences, North Carolina State University, Raleigh, NC, USA

Background: Conventional, effective treatment of high-grade atrioventricular block (AVB) involves a single endocardial pacing lead positioned near the right ventricular apex (RVA). Other pacing sites might produce less cardiac dyssynchrony and better left ventricular (LV) function.

Hypothesis/Objectives: Endocardial pacing at the cranioventral RV outflow tract (RVOT) might differ hemodynamically from RVA pacing.

Animals: Client-owned dogs (n = 8) with high-grade AVB.

Methods: Prospective, within-subjects comparisons (paired t-tests) of select ECG, LV synchrony and systolic function indices were made between pacing sites. Single plane (apical 2-chamber) transesophageal echocardiography (TEE) and multiple-lead ECG recordings were obtained. After transitioning from transcutaneous to temporary endocardial pacing using the permanent lead, data were collected at 100 pulses/minute following a standardized acclimation period during both RVOT and RVA pacing (Table). LV global and endocardial longitudinal strain (GLS, ELS), SD of time to peak strain, single-plane ejection fraction (EF) and stroke volume, and QRS duration were measured/calculated.

Results: Mean EF was higher in the RVOT (P = 0.02). ELS for RVOT pacing was −23.1% vs. −20.4% for the RVA (P = 0.072) but with no difference in mean GLS. QRS durations were longer in the RVOT site. No intra- or postoperative complications occurred.

Conclusions and Clinical Importance: This feasibility study was not sufficiently powered to evaluate superiority of lead positioning, but the data to test this hypothesis can be obtained safely, ideally with multiple LV planes and endocardial ECG recordings.

¹North Carolina State University, Raleigh, NC, USA; ²Texas A&M University, College Station, TX, USA

Background: Anemia is an independent negative prognostic indicator in dogs with congestive heart failure, representing a target for improving quality of life and survival. Gastrointestinal bleeding may potentiate anemia in dogs with heart failure from myxomatous mitral valve disease (MMVD). Potential risk factors for gastric ulcerations and erosions (GUE) with MMVD include acquired platelet dysfunction from loss of functional von Willebrand factor (vWF) due to shear stress from mitral regurgitation and chronic intestinal hypoperfusion from decreased cardiac output.

Hypothesis/Objectives: Dogs with MMVD stage C have more GUE compared to age-matched controls.

Animals: Six client-owned MMVD stage C and five healthy dogs enrolled. Exclusion criteria included liver, kidney, or GI disease and antibiotic, steroid, NSAID, or gastric acid suppressant use within 21 days.

Methods: Prospective case-control study evaluating GI mucosa by video capsule endoscopy (VCE), platelet closure time (PC), vWF antigen assay, and complete blood count. Blinded investigator performed VCE scoring.

Results: All MMVD dogs had GUE, three of which had diffuse GUE. Five had irregular/thickened mucosa. Four healthy dogs had GUE defined as single, few, or multiple with no diffuse GUE, and only two had irregular mucosa. PCV and vWF antigen assay did not differ between groups. Dogs with MMVD had significantly increased PC with ADP/collagen compared to controls (P = 0.0143, Wilcoxon exact test).

Conclusions and Clinical Importance: Dogs with MMVD stage C had more severe GUE and irregular gastric mucosa, and platelet dysfunction might be a contributing factor. Larger studies should assess overall prevalence as well as potential therapeutic options.

¹College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA; ²Professor, Cardiology and Interventional Medicine, College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA; ³Alumni Professor, College of Veterinary Medicine, Auburn University, Auburn, AL, USA; ⁴Associate Professor, College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA; ⁵Associate Professor, Small Animal Emergency and Critical Care, College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA

Background: Arterial thromboembolism is a devastating consequence of hypertrophic cardiomyopathy (HCM) in cats due to left atrial (LA) enlargement and dysfunction. Prevention of ATE relies on anticoagulant medication, rather than improving atrial transport function.

Hypothesis: Pimobendan improves LA systolic function in cats with HCM and LA enlargement.

Animals: 14 client-owned cats with stage B2 HCM.

Methods: Prospective, double-blind, placebo-controlled clinical study. Echocardiographic assessment of left atrial and left auricular systolic function was performed before and one hour after administration of a single oral dose of pimobendan (0.3 mg/kg). Plasma concentrations of pimobendan and o-desmethyl-pimobendan (ODMP) were also analyzed.

Results: Nine cats received pimobendan and 5 placebo. Preliminary data analysis demonstrated that LA size based on LA area (cm²) (3.70 ± 1.27 vs. 3.10 ± 0.81; P = 0.08, power = 0.24) and LA volume (cm3) decreases (5.11 ± 2.54 vs. 4.55 ± 2.36; P = 0.19, power = 0.17), left auricular flow velocity (m/s) increases (0.34 ± 0.15 vs. 0.50 ± 0.29, P = 0.14, power = 0.20), and pulmonary venous atrial reversal flow velocity (m/s) increases (0.31 ± 0.11 vs. 0.36 ± 0.14, P = 0.08, power = 0.32) after pimobendan. Compared to the 6/8 cats with expected plasma concentrations (ng/mL) of pimobendan one hour after administration (7.57–33.98) and ODMP (2.75–11.23), plasma concentrations in 2 cats were notably lower (pimobendan 1.71 and 0.43 ng/mL and ODMP not detectable).

Conclusions: Pimobendan may reduce LA size and improve LA transport function in cats with HCM and LA enlargement, but larger a number of cats need to be studied.

The Ohio State University, Columbus, OH, USA

Background: The size of the ascending aorta (aortic root) is of clinical relevance, in particular in cats with systemic hypertension and as a variable of the left atrium-to-aortic ratio, used in the echocardiographic diagnosis of left atrial enlargement.

Hypothesis/Objectives: Determine reference values and 95% prediction intervals for two-dimensional echocardiographic variables of aortic root size in cats. We hypothesized that dimensions of the aortic root in healthy cats are mainly dependent on body weight and age.

Animals: 220 healthy cats.

Methods: Retrospective observational study. Systolic and diastolic dimensions of the aortic valve, the sinus of Valsalva, the sinotubular junction, and the ascending aorta and sinus height were evaluated. Reference values and 95% prediction intervals were determined using raw data and values after allometric transformation. The effect of body weight and age was determined using multivariable regression analysis.

Results: Proportionality constants (κ), 95% prediction intervals, and allometric scaling exponents (b) were computed for all variables, and reference values and prediction intervals determined. Body weight and age, but not sex and breed, were independent predictors of aortic root size. Cats >12 years old had significantly (adjusted P < 0.05) increased echocardiographic variables of aortic root size compared to cats 1–2 years old, >2–6 years old, and >6–12 years old.

Conclusions and Clinical Importance: Reference and prediction intervals of echocardiographic variables characterizing aortic root size in cats are provided. The effect of body weight and age has to be considered for clinical decision-making when using these variables in clinical practice.

¹University of Illinois at Urbana Champaign, Champaign, IL, USA; ²Cardiology Resident, Veterinary Clinical Medicine, University of Illinois, IL, USA; ³Cardiology Specialty Intern, MSPCA Angell Animal Medical Center; ⁴Veterinary Student, Texas A&M University, College Station, TX, USA; ⁵Cardiology Research Intern, Veterinary Clinical Medicine, University of Illinois, IL, USA; ⁶Clinical Assistant Professor, Veterinary Clinical Medicine, University of Illinois, IL, USA; ⁷Professor Cardiology, Eugene Ch’en Chair in Cardiology, Small Animal Clinical Sciences, Texas A&M University, College Station, TX, USA

Background: Circulating N-terminal pro-B-type natriuretic peptide (NT-proBNP) concentrations accurately discriminate congestive heart failure (CHF) from non-cardiac respiratory dyspnea (NC-RD), yet quantitative results may take >48 h. Our objective was to determine if the quantitative Bionote Vcheck point-of-care (POC) NT-proBNP serum assay accurately discriminates CHF versus NC-RD in dogs and cats.

Hypothesis: Quantitative POC NT-proBNP will accurately discriminate CHF versus NC-RD in dogs and cats.

Animals: Sixty-nine dogs and 40 cats from 2 university hospitals.

Methods: In this prospective cross-sectional study, serum NT-proBNP concentrations were measured in client-owned dogs and cats presenting for dyspnea. Categorization of CHF was based on echocardiographic cardiac disease and edema or effusion that resolved with diuretic treatment. Normality was assessed using a Shapiro-Wilk test, and groups were compared using a Mann-Whitney test and receiver operating curves. A P < 0.05 was considered significant.

Results: CHF animals had higher (P < 0.001) median NT-proBNP concentrations (cat, 1293 pmol/L; dog, 3107 pmol/L) compared with NC-RD (cat, 49 pmol/L; dog, 726 pmol/L). ROC analysis indicated excellent discriminatory ability in dogs (AUC = 0.97, P < 0.0001) and cats (AUC = 0.99, P < 0.0001). An optimal cutoff in dogs of >1900 pmol/L achieved a sensitivity of 85% and specificity of 95%. An optimal cutoff in cats of >272 pmol/L achieved a sensitivity of 100% and specificity of 94%.

CONCLUSION AND CLINICAL IMPORTANCE: The Bionote Vcheck NT-proBNP assay is an accurate quantitative POC test that may be helpful in the immediate assessment of dyspneic dogs and cats.

JASMINE Veterinary Cardiovascular Medical Center, Japan

Background: Mitral valve repair (MVR) could be a curative treatment for myxomatous mitral valve disease (MMVD) in dogs. Previous reports in medical treatment have suggested that Cavalier King Charles Spaniels (CKCS) might be more susceptible to developing MMVD than other breeds, but the breed-specific characteristics and the long-term outcomes of MVR are unclear.

Hypothesis/Objectives: We investigated the differences in cardiac reverse-remodeling and survival for MVR in different breeds.

Animals: We retrospectively analyzed the data of dogs with MMVD that underwent MVR from February 2017 to February 2019 at our center.

Methods: Based on breeds, dogs were divided into three groups: Chihuahuas, CKCS, and others. Thoracic radiographs and echocardiography were evaluated in the preoperative period and 6, 12, and 36 months post-surgery.

Results: Our study included 444 dogs (Chihuahuas = 206, CKCS = 40, and others = 198). CKCS group had significantly higher vertebral heart score, left atrial aortic root ratio, and diastolic left ventricular normalized dimension both pre- and post-surgery. The three-year survival rate for all-cause mortality derived by the Kaplan-Meier curve was not different among the three groups: 75%, 66%, and 67%, respectively (P = 0.12; log-rank test).

Conclusions and Clinical Importance: Postoperative reverse remodeling might differ, especially in CKCS. Thus, early surgical intervention might be better for improving reverse remodeling in CKCS. However, MVR improves survival in all breeds despite differences in heart size.

¹University of Minnesota, MN, USA; ²Veterinary Medical Center, University of Minnesota, MN, USA; ³College of Veterinary Medicine, University of Minnesota, MN, USA; ⁴MedVet Cincinnati, Cincinnati, OH, USA; ⁵Animal Emergency and Referral Center of Minnesota, MN, USA; ⁶The Ohio State University, OH, USA; ⁷University of Georgia, GA, USA; ⁸University of Wisconsin, WI, USA

Background: Ventricular preexcitation (VPE) occurs when atrial electrical impulses prematurely excite the ventricles through aberrant muscle bundles known as accessory pathways (AP). Orthodromic atrioventricular reciprocating tachycardia (OAVRT) is a re-entrant narrow complex tachyarrhythmia maintained by an AP.

Hypothesis/Objectives: To describe signalments, clinical signs, electrocardiographic and diagnostic imaging features, treatments, prognostic variables, and outcomes in cats with VPE. We hypothesized that cats with VPE are at risk for developing OAVRT and associated clinical signs. Negative prognostic indicators were hypothesized to include presence of clinical signs and structural heart disease.

Animals: Twenty-three cats diagnosed with VPE between January 2010 and August 2022.

Methods: Retrospective, multicenter study. VPE diagnosis was based on ECG evidence of reduced PR interval and delta wave QRS morphology. Median survival time (MST) was estimated by Kaplan-Meier curve.

Results: Fourteen (60.8%) cats with VPE had OAVRT documented on ECG and 4/23 (17.4%) had suspected OAVRT based on associated clinical signs. Common presenting signs included collapse (15/23; 65.2%) and respiratory distress (14/23; 60.8%). Five cats (21.7%) were asymptomatic. ECG during VPE revealed a reduced PR interval (median 40 ms; range 20–45 ms) and prolonged QRS duration (median 60 ms; range 45–90 ms). Heart rate during OAVRT ranged from 310–420 bpm (median 375 bpm). Treatment included atenolol (10/18), sotalol (5/18), diltiazem (2/18), and amiodarone (1/18). MST from date of diagnosis was 1872 days.

Conclusions and Clinical Importance: The majority of cats in this study with VPE had clinical OAVRT. The prognosis for cats with VPE is considered fair with MST >5 years.

¹School of Veterinary Medicine, University of California, Davis, CA, USA; ²Professor of Clinical Animal Behavior, Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, USA; ³Resident of Cardiology, Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, USA; ⁴Department of Public Health Sciences, School of Medicine, University of California, Davis, CA, USA; ⁵Assistant Professor of Cardiology, Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, USA

Oral trazodone is used as an anti-anxiety medication in dogs prior to veterinary visits; however, the effects on cardiac diagnostics are not well studied. The purpose of this study was to investigate the effects of oral trazodone on blood pressure (BP), echocardiography, electrocardiography, and behavior in healthy dogs.

15 healthy, client-owned, adult dogs aged 1–8 years were enrolled in this prospective, double-blinded, placebo-controlled, crossover study. Dogs were randomized to receive placebo or trazodone (9.2–11.2 mg/kg) orally 90–120 min before arrival. Physical examination, Doppler BP, electrocardiogram, echocardiogram, and 24-h Holter placement were performed. After a minimum 7-day wash-out period, diagnostics were repeated with the alternate treatment. Stress scores were obtained using owner questionnaires and a blinded review of video obtained during visits. For normally distributed data, a two-sample t-test for comparison of means between drugs was performed.

Blood pressure was significantly decreased following trazodone (mean ± SD, 128.7 ± 22.3 vs. 143.4 ± 26.61, P = 0.02). Measurements of left atrial size, left ventricular size and function, and corrected QT interval were not significantly different. Average 24-h heart rate was not significantly different. Median (interquartile range) of ventricular ectopy was 0 (0–2) for both groups. Owner-reported stress and average video-scored stress were significantly decreased following trazodone (P = 0.005 and P = 0.003). Adverse effects reported with trazodone were sleepiness (12/15), decreased appetite (4/15), and ataxia (1/15).

In conclusion, a single, oral, pre-visit dose of trazodone is well-tolerated and reduces signs of stress in dogs. Trazodone causes mild reduction in BP and clinically insignificant echocardiographic and electrocardiographic changes.

¹University of Illinois, Urbana, IL, USA; ²Cardiology Resident, University of Illinois, Urbana, IL, USA; ³Cardiology Resident, Veterinary Clinical Medicine, University of Illinois, Urbana, IL, USA; ⁴Clinical Assistant Professor, Veterinary Clinical Medicine, University of Illinois, Urbana, IL, USA; ⁵Assistant Professor, Veterinary Clinical Medicine, University of Illinois, Urbana, IL, USA

Background: With new interventional procedures aimed at treating degenerative valve disease, the need to stratify patients into surgical categories is necessary. Some methods for determining regurgitant fraction require accurate quantification of mitral annular area (MAA). This retrospective study evaluated MAA with standard two-dimensional (2D) transesophageal (TEE) measurements compared with three-dimensional (3D) planimetry.

Hypothesis: 2D orthogonal views will most closely approximate MAA compared with the reference standard 3D planimetry.

Animals: Thirty-two dogs of variable breed and size

Methods: All TEE studies were performed as part of catheter-based interventions including congenital disease and transcatheter edge-to-edge mitral valve repair (TEER). Studies were reviewed using 3D planimetry and traditional apical 2D views: 2-chamber (2CH), 4-chamber (4CH), commissural (CC), and anterior-posterior (AP). Data were assessed for normality using a Shapiro-Wilk test. Continuous variables comparing 2D with 3D planimetry were assessed using a Friedmean test with Dunn's multiple comparisons, Spearman rank correlation, and Bland-Altman plots. A P < 0.05 was considered significant.

Results: Two-dimensional apical 2CH and 4CH MAA and orthogonal 4Ch/2CH and CC/AP ellipse MAA were not significantly different than planimetry. There was significant correlation between planimetry and 4CH (r = 0.95, P < 0.001), 2CH (r = 0.92, P < 0.01), 4CH/2CH (r = 0.97, P < 0.0001), and CC/AP (r = 0.99, P < 0.0001). Among these variables CC/AP had the smallest bias (0.09–0.37) and closest limits of agreement (−0.63 to 0.81) with planimetry.

Conclusion and Clinical Importance: Two-dimensional CC/AP derived MAA is an acceptable alternative to 3D planimetry in dogs.

¹School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI, USA; ²Clinical Professor, Cardiology, Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI, USA

Background: Dogs with atrial fibrillation (AF) live longer with strict heart rate control (SHRC, 24-hour mean heart rate ≤125 beats/minute). Although amiodarone (AM) and diltiazem (DTZ) are used to lower ventricular response rate in dogs with AF, information about their relative efficacy for achieving SHRC is lacking.

Hypothesis/Objectives: Determine if therapy with AM, DTZ or a combination will achieve SHRC in dogs with AF.

Animals: Twelve client-owned dogs with newly-diagnosed AF were enrolled and returned for follow-up.

Methods: Prospective, randomized, non-blinded clinical trial. Eligible dogs had AF with mean daily heart rate (MDHR) >125 beats/minute (baseline, 24-h Holter) and were randomly assigned to receive AM or DTZ at standard doses. Repeat 24-h Holter assessments were performed at 3, 6 and 9–21 weeks after starting treatment. If MDHR >125 beats/minute at any assessment, the second drug was added.

Results: Six dogs each received AM or DTZ first. MDHR decreased significantly after AM (P = 0.03) or DTZ (P = 0.05) initiation; 1 dog in each group achieved SHRC at 3 weeks. At last follow-up, 11/12 dogs were receiving combined AM/DTZ for median [range] 50 [20–53] days with no difference based on which drug was initiated first (P = 0.87). Most dogs (7/11, 64%) had not achieved SHRC (139 [94–160]) beats/minute at standard doses (AM, 7.5 [6.2–9.3] mg/kg/day; DTZ, 7.3 [6.3–11.9] mg/kg/day).

Conclusions and Clinical Importance: Monotherapy with AM or DTZ or combination therapy of AM/DTZ does not achieve SHRC in most dogs with AF.

¹Veterinary Teaching Hospital, Colorado State University, Ft. Collins, CO, USA; ²Cardiology and Cardiac Surgery, Veterinary Teaching Hospital, Colorado State University, Ft. Collins, CO, USA

Background: Stent implantation is an emerging therapy for congenital pulmonary valve stenosis (PS) in dogs.

Hypothesis/Objectives: Describe two operators experience with balloon-expandable (BE) transpulmonary stents for PS at a single institution.

Animals: 60 dogs with PS, including French bulldogs (n = 28), English bulldogs (7), pit bulls (6), other breeds (19).

Methods: Retrospective analysis of medical records.

Results: All dogs survived to discharge. The mean (±SD) age at time of intervention was 22.4 ± 19.9 months (max, min = 3, 104) at a weight of 12.8 ± 6.6 kg (4.2, 30.9). Anomalous coronary anatomy was present in 7 dogs. Nineteen dogs were in congestive heart failure at time of intervention. For 41 dogs, transpulmonary stent implantation was their first PS intervention, while 19 dogs had previously undergone balloon pulmonary valvuloplasty that was deemed ineffective. Seven different BE stent designs were implanted, with a 10 mm diameter bare metal stent being the most common in 40 dogs; 3 cases received covered stents. Vascular access varied from 7 Fr to 14 Fr. Pre-mounted stents were selected in 48 cases; 12 cases used hand-crimped stents. Post-dilation was performed in 17 dogs. A balloon-in-balloon delivery catheter was used in 10. Echocardiographically-derived peak systolic pressure gradients were 133 ± 44 mm Hg (60, 248) prior to stenting and 53 ± 28 mm Hg (10, 180) the next day for an average reduction of 58% ± 22% (0%, 90%).

Conclusions: Stent implantation is feasible for dogs with PS, effecting a clinically relevant reduction in pressure gradient at time of discharge.

¹School of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, TX, USA; ²Dog Aging Project, Laboratory Medicine & Pathology, School of Medicine, University of Washington, Seattle, WA, USA; ³DAP Consortium, Dog Aging Project, Laboratory Medicine & Pathology, School of Medicine, University of Washington, Seattle, WA, USA; ⁴Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA, USA

Background: There is little published research on prevalence of subclinical disease and cardiovascular abnormalities in apparently healthy mature adult dogs.

Hypothesis/Objectives: To describe prevalence of subclinical disease and cardiovascular examination abnormalities, and reasons for participant exclusion, in dogs screened for a clinical trial.

Animals: Reportedly healthy, client-owned, mature adult (>7-year-old) dogs screened for a large, prospective, randomized multicenter clinical trial.

Methods: Prior to in-clinic screening, electronic medical records of owner-nominated dogs were reviewed for evidence of systemic illness or treatment with an exclusionary drug. For each, signalment, body weight, and reason(s) for exclusion were recorded. For dogs subsequently screened in-person, indirect systolic arterial blood pressure (SBP), heart murmur presence, findings of echocardiography and electrocardiography, and any reason(s) for exclusion were recorded.

Results: 90 (29%) of 310 dogs were excluded prior to in-clinic screening, most commonly for exclusionary drugs or diagnoses (40.0% and 34.4% of excluded dogs, respectively). 50 (41%) of 121 dogs screened in-clinic were excluded, most commonly for a clinically significant cardiovascular or biospecimen abnormality (50% and 20% of excluded dogs, respectively). Degenerative mitral valve disease (DMVD) was diagnosed in 38 (33%) of 116 dogs undergoing echocardiography; of these, 18 (47%) had a heart murmur. Premature ventricular ectopy was documented in 20 (17%) of 117 dogs undergoing electrocardiography.

Conclusions and Clinical Importance: Cardiovascular abnormalities were common in this apparently healthy sample of mature adult dogs. Absence of a heart murmur in many dogs with DMVD suggests poor sensitivity of auscultation for this condition.

¹Chuan Animal Hospital; ²Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, Medford, MA, USA

Background: Acute cardiogenic pulmonary edema (CPE) is a serious development for dogs with myxomatous mitral valve disease (MMVD), and CPE commonly requires hospitalization.

Hypothesis/Objectives: To characterize clinical findings and evaluate risk factors in dogs with MMVD hospitalized with acute CPE.

Animals: 100 dogs with MMVD hospitalized with acute CPE.

Methods: Prospective observational study measuring clinical parameters and Tufts Dyspnea Score (TDS) within the first 24 h of hospitalization to assess outcomes. Descriptive statistics and regression analysis were used.

Results: Upon hospital presentation, median respiratory rate was 64 bpm and median TDS was 5 (TDS range 0 to 10). Median length of stay in the ICU was 20 h. Nighty-five of 100 dogs survived to hospital discharge. For the 91 dogs with follow-up information, 39 experienced death or re-hospitalization for CPE within 2 months after hospital discharge. No clinical parameter at hospital presentation predicted survival to hospital discharge. The lowest recorded TDS within the first 12 h (TDS ≦4) had a sensitivity of 97.9% and specificity of 80% for predicting survival to hospital discharge. Dogs with a louder murmur at presentation or a persistently high respiratory rate within the first 12 h were more likely to have an adverse two-month outcomes.

Conclusions and Clinical Importance: We observed a high survival rate in dogs with MMVD hospitalized with acute CPE. No clinical parameter at hospital presentation predicted survival to hospital discharge, however, parameters recorded during the initial 24 h of hospitalization did predict hospital discharge and adverse two-month outcomes.

¹Davies Veterinary Specialists, Shillington, UK; ²Department of Engineering, University of Cambridge, Cambridge, UK; ³Department of Veterinary Medicine, University of Cambridge, Cambridge, UK; ⁴Royal Veterinary College, London, UK

Background: A heart murmur is a key clinical feature of canine degenerative valve disease (DVD). Recent machine learning algorithms, combined with electronic stethoscopes, have shown promise at detecting heart murmurs in people, but further evidence is needed of their application to canine heart sounds.

Hypothesis/Objectives: To train and evaluate a machine learning algorithm to detect and grade heart murmurs in dogs, using recordings from an electronic stethoscope.

Animals: 470 client-owned dogs (266 DVD, 132 other cardiac diseases, 72 normal) undergoing routine echocardiography at four referral centers.

Methods: Diagnostic method development and assessment. For each dog, a board-certified cardiologist or cardiology resident used an electronic stethoscope to grade murmurs and make 15-second recordings at three auscultation sites (left apex, left base, right side). A recurrent neural network, originally developed for human murmur detection, was then retrained to predict the cardiologist's murmur grade from the sound recording.

Results: On an unseen half of the data set, the neural network detected a murmur of any grade with an area under the receiver operating characteristic of 0.907 (95% CI 0.887–0.927), with an operating sensitivity of 89.3% (95% CI 85.1%–93.5%) and specificity of 74.9% (95% CI 66.7%–83.0%). The individual Levine murmur grade was predicted with a mean absolute error of 0.648 (95% CI 0.602–0.694).

Conclusions and Clinical Importance: The algorithm demonstrates good agreement with cardiologists, potentially enabling a non-expert user to perform accurate murmur screening and grading.

¹College of Veterinary Medicine, Seoul National University, Seoul, South Korea; ²Clinical Professor, Large Animal Clinical Sciences, University of Florida, Gainesville, FL, USA; ³Clinical Professor Cardiology, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA; ⁴Clinical Assistant Professor, Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA; ⁵Professor of Cardiology, Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA; ⁶Clinical Assistant Professor, Cardiology, Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA; ⁷Clinical Veterinarian/Interventional Center, Korea Animal Medical Center, Chungcheongbuk-do, South Korea; ⁸Clinical Veterinarian, 24h Daejeon Animal Medical Center Soop; ⁹Clinical Veterinarian, Bone Animal Medical Center; ¹⁰Clinical Veterinarian, Lucid Animal Medical Center, Gangbuk-gu, Seoul, South Korea; ¹¹Clinical Veterinarian, Poom Animal Medical Center; Clinical Veterinarian, Ansim Animal Medical Center; ¹³Clinical Veterinarian/Emergency Medicine, Department of Clinical Science, College of Veterinary Medicine, Seoul National University, Seoul, South Korea

Background: The Amplatz canine duct occluder (ACDO) is commercially available for PDA occlusion, however, additional small animal-specific devices are still needed to address current device limitations regarding patient size or ductal morphology. We have developed a new device designed to occlude the PDA of dogs. The system is self-contained with a side-port for angiography, optimal sheath curvature, and is designed to reduce catheter and wire exchanges. The sheath is 5 Fr and can accommodate 6–10 mm occluders.

Hypothesis/Objectives: The new system and occluder can be introduced into the right femoral artery and successfully deployed into the ductus of dogs >1.5 kg with Type IIa or IIb left-to-right shunting PDA under fluoroscopic guidance.

Animals: Client owned ten dogs with PDA from May 2021 to January 2023.

Methods: We retrospectively evaluated the system in 10 dogs with PDA. Occluder size and procedural time were recorded. Echocardiography was used to evaluate the completeness of the PDA occlusion at 1 day and 1-, 3- and 6-months post-procedure.

Results: Mean body weight was 3.14 kg (1.5–4.6 kg). Occluder sizes used were 6mm (n = 4), 8 mm (n = 2), and 10 mm (n = 4). Excluding anesthesia, mean procedure time was 25 min (20–30 min). Occlusion of the PDA was complete at 1 day in 3 dogs and by 1 month in 5 dogs. Residual flow was found in 2 dogs at 3 months but resolved by 6 months.

Conclusions and Clinical Importance: This study shows that the new PDA occluder system is effective in small dogs requiring 6–10 mm occluders.

Title: Use of a newly developed vascular occluder system for closing patent ductus arteriosus in dog.

Figure 1. A newly developed occluder system.

JASMINE Veterinary Cardiovascular Medical Center, Yokohama, Japan

Background: Mitral valve repair (MVR) could be a curative treatment for myxomatous mitral valve disease in dogs, and cardioplegic solutions play an essential role in its procedure. However, procedure methodologies are not well established, and complications have not been clarified yet.

Hypothesis/Objectives: We hypothesized that the incidence of ventricular fibrillation (VF), the main complication of reperfusion injury after cross-clamping, might be lower with blood cardioplegia (BCP) than with crystalloid cardioplegia (CCP).

Animals: A total of 251 client-owned dogs who underwent MVR by a single surgeon from November 2015 to November 2017 were included.

Methods: We retrospectively analyzed the dogs’ surgical records, including VF incidence, use of transfusion, and cross-clamping time, as well as echocardiographic measurements obtained before and 1-month after surgery. Dogs were divided into two groups according to the type of cardioplegia, CCP and BCP.

Results: Logistic regression analysis showed that group CCP (odds ratio [OR] = 2.20, confidence interval [CI] = 1.06–4.57; P = 0.03) and cross-clamping time (OR = 1.04, CI = 1.01–1.06, P < 0.01) were associated with AF. In addition, group CCP (OR = 2.52, CI = 1.19–5.32, P = 0.02) and low body weight (OR = 0.58, CI = 0.49–0.69, P < 0.01) were associated with transfusion use. There was no difference between the groups in the pre- and postoperative echocardiographic measurements.

Conclusions and Clinical Importance: The BCP group had a lower incidence of VF and less use of blood transfusion than the CCP group. This finding indicates that BCP is a superior cardioplegic technique for MVR in dogs.

¹College of Veterinary Medicine, University of Georgia, Athens, GA, USA; ²Associate Professor, Masonic Children's Hospital, University of Minnesota, Minneapolis, MN, USA; ³Professor, Colorado State University, Ft. Collins, CO, USA; ⁴Clinical Associate Professor, University of Wisconsin, Madison, WI, USA; ⁵Pediatric Nurse Practitioner, Cardiac Cath Lab, Children's Healthcare of Atlanta, Atlanta, GA, USA; ⁶Associate Professor, University of Georgia, Athens, GA, USA; ⁷Clinical Assistant Professor, University of Wisconsin, Madison, WI, USA; ⁸Physician Assistant, Masonic Children's Hospital, University of Minnesota, Minneapolis, MN, USA; ⁹Research Technician, University of Georgia, Athens, GA, USA; ¹⁰DVM Student, Colorado State University, Ft. Collins, CO, USA; ¹¹University of Wisconsin, Madison, WI, USA; ¹²Professor, Children's Healthcare of Atlanta, Emory University School of Medicine, Atlanta, GA, USA

Background: Transcatheter therapeutics have revolutionized management of patent ductus arteriosus (PDA) in children and animals. Further understanding of interventions for PDA across species may help improve outcomes for both.

Hypothesis/Objectives: To describe characteristics and outcomes of PDA in patients undergoing transcatheter occlusion in pediatric and veterinary populations.

Animals: 202 human patients from two pediatric cardiology centers and 106 dogs from three veterinary cardiology centers.

Methods: Multicenter, retrospective review analyzing data of PDA patients between July 1, 2019–June 30, 2021. Demographics, procedural characteristics, and outcomes were assessed.

Results: Active or historical congestive heart failure was present in 45/202 (23%) humans and 19/106 (18%) dogs prior to catheterization (P = 0.40). A transvenous approach from the right femoral vein was most common in 173/202 (86%) humans, compared to a transarterial approach using the right femoral artery in 101/106 (95%) dogs. Anticoagulant use during human intervention 165/165 (100%) significantly differed from canine intervention 2/103 (2%) (P < 0.0001). Vascular closure techniques differed with manual compression in all humans versus vessel ligation in 76 (73%) and vessel repair in 25 (24%) dogs following vascular cut-down; an additional 2 (2%) dogs underwent suture-based percutaneous closure and 1 dog (1%) manual compression (P < 0.0001). Successful intervention (appropriate device deployment) was seen in 98% of humans compared to 93% of dogs (P = 0.051).

Conclusions: Humans and dogs have similar success rates during transcatheter PDA occlusion. Roughly 1 in 5 patients of both species have congestive heart failure at the time of catheterization. Anti-coagulation is more commonly used in humans than dogs.

University of Minnesota, Minneapolis, MN, USA

Background: The Amplatz Canine Duct Occluder (ACDO) is routinely used for Patent Ductus Arteriosus (PDA) occlusion. Limited data is available on clinical outcomes and success rates with ACDO device placement.

Objectives: To report clinical outcomes and complications of standard ACDO procedures in a large cohort of dogs.

Animals: Dogs presenting to the University of Minnesota from 2008–2022 that underwent ACDO device placement for PDA occlusion.

Methods: Retrospective analysis of outcomes and complications in dogs receiving the ACDO device. Echocardiography was performed prior to occlusion, 24-h post-occlusion and during follow-up recheck visits. Procedural success was determined by occlusion of flow on angiography, color, and spectral Doppler.

Results: 181 dogs underwent ACDO device placement. Dogs had a median weight of 6.5 kg (range 2.55–60.5 kg) and required a median device size of 6 mm (range 3–14 mm). At 24-h post-occlusion, 4.4% (8/181) had trivial flow through the device. Trivial flow was noted on recheck in 6% (7/116) of patients with a median follow-up time of 116 days (range 24–4595 days). Complications occurred in 6.1% (11/181), with 2% (5/181) considered minor. Major complications occurred in 3.3% (6/181) including device embolization (n = 1), hemorrhage from femoral access site requiring transfusion (n = 1), cardiac arrest postoperatively (n = 1), femoral artery tear (n = 1), external iliac artery tear (n = 1), and wire perforation of the aorta (n = 1). Overall procedural mortality rate was 1.1% (2/181).

Conclusions: The high procedural success and low complication rates support use of the ACDO device as a safe and effective treatment for PDA occlusion in dogs.

¹Oregon State University, Corvallis, OR, USA; ²Associate Professor, Cardiology, Oregon State University, Corvallis, OR, USA

Background: Trazodone, a serotonin antagonist and reuptake inhibitor (SARI) with alpha-adrenergic blocking effects, is an anxiolytic increasingly administered to dogs prior to veterinary visits. While trazodone appears to be well tolerated in dogs, its effects on echocardiographic and hemodynamic parameters are largely unknown.

Hypothesis/Objectives: To assess the effects of trazodone on blood pressure (BP), heart rate (HR), echocardiographic measurements, and sedation level in healthy dogs.

Animals: 31 adult dogs considered healthy based on physical exam (PE), M-mode and two-dimensional (2D) echocardiography, electrocardiogram (ECG), BP, blood chemistry, and urinalysis.

Methods: Prospective, double-blinded clinical trial. Dogs were randomized to receive standard (3–5 mg/kg) or high dose (10–12 mg/kg) trazodone at home 120–180 min prior to presentation. A washout period of at least 48 h was mandated between doses. Sedation level, PE, BP, and echocardiography were performed at each visit.

Results: No clinically significant differences were found between baseline, standard, or high dose trazodone for HR, BP, or echocardiographic parameters including linear and volumetric left atrial and ventricular size and indices of systolic and diastolic function. There was a significant increase in sedation score between baseline (median 0, range 0–1) and standard dose (median 1, range 1–3) and between baseline and high dose (median 1, range 1–3) with no significant difference between standard and high dose.

Conclusion: A single dose of trazodone up to 12 mg/kg produces mild sedative effects in dogs within 120–180 min of administration and clinically insignificant changes to echocardiographic measurements, BP, and HR.

University of Illinois

Background: Patent ductus arteriosus (PDA) is the most common cardiac congenital defect in dogs and with timely correction carries a good prognosis. If closure is delayed, the risk for heart failure and death increase. This study evaluated the short-term hemodynamic effects of pimobendan in dogs with preclinical left-to-right shunting PDA.

Hypothesis: Pimobendan will provide hemodynamic benefits in dogs with left-to-right shunting PDA.

Animals: 17 dogs with preclinical PDA.

Methods: For this prospective observational cohort study, patients were evaluated via physical examination, thoracic radiographs, quantitative N-terminal pro-brain natriuretic peptide, and transthoracic echocardiography. Dogs were eligible based on the following criteria: echocardiographic evidence of a PDA (left-to-right) regardless of anatomic classification, the presence of cardiomegaly defined as left atrial (LA) and left ventricular (LV) size exceeding the 95% predictive interval, and radiographic cardiomegaly (VHS >10.5) without concurrent pulmonary edema. All patients received pimobendan (0.4–0.6 mg/kg/day divided into q 12 h dosing). Re-evaluation of all tests was performed on day 7 prior to PDA closure. Data were assessed for normality using a Shapiro-Wilk test and pre-post variables were compared using a paired t-test or a Wilcoxon signed-rank test when appropriate. A P < 0.05 was considered significant.

Results: No patients decompensated during the study and significant differences in VHS (−0.2), LA volume (−0.31 mL/kg), normalized LV diastolic (−0.45 mL/kg) and systolic (−0.54 mL/kg) volume, LV ejection fraction (+6.1%), and NT-proBNP (−332 pmol/L) were observed.

Conclusion and Clinical Importance: Pimobendan may provide short-term hemodynamic benefit in preclinical PDA patients.

¹Hokkaido University, Sapporo, Japan; ²Associate Professor, Hokkaido University, Sapporo, Japan; ³Associate Professor, Rakuno Gakuen University, Ebetsu, Japan; ⁴Academic Fellow, Hokkaido University, Sapporo, Japan; ⁵Professor, Hokkaido University, Sapporo, Japan

Background: Cardiac disease cause hepatic congestion and fibrosis, which increase liver stiffness (LS). LS can be estimated by 2D-Shear Wave Elastography (SWE), which measures shear wave speed (SWS), an index of viscoelasticity and dispersion slope (DS), an index of viscosity. In the liver, fibrosis elevates elasticity, while congestion or inflammation elevates viscosity.

Hypothesis/Objectives: To analyze SWE-measured LS in dogs with cardiac disease and to identify its determinants.

Animals: Sixty-five client-owned dogs with cardiac disease.

Methods: In this cross-sectional prospective study, SWS and DS were measured using 2D-SWE in all dogs along with the short to long diameter ratio of the caudal vena cava (CVC SD/LD), an index of congestion, and the left ventricular outflow tract velocity time integral (LVOT-VTI), an index of cardiac output by echocardiography. The discriminatory ability of these parameters for right heart failure (RHF) was compared using ROC analysis. The relation of SWS and DS to other echocardiographic indices was evaluated by multiple regression analysis.

Results: SWS, DS, and CVC SD/LD were all significantly higher, while LVOT-VTI was significantly lower in the dogs with RHF. DS had the highest accuracy in discriminating RHF (AUC = 0.998), followed by SWS (AUC = 0.992). In multiple regression analysis, CVC SD/LD was the most related factor to the SWS and DS followed by LVOT-VTI.

Conclusions and Clinical Importance: Elevated SWS and DS in dogs with RHF reflects congestion and reduced cardiac output. 2D-SWE may be useful to predict the presence of hepatic congestion and RHF in dogs with cardiac disease.

¹College of Veterinary Medicine, University of Georgia, Athens, GA, USA; ²Assistant Professor of Cardiology, Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA, USA; ³Clinical Professor—Cardiology, Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA; ⁴Intern, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA; ⁵Associate Professor of Cardiology, Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA, USA

Background: Pulmonary valve stenosis (PS) is often treated with balloon pulmonary valvuloplasty (BPV) if moderate or severe. While Doppler echocardiographic assessment of transpulmonary pressure gradient (PG) serves as a surrogate for catheter-based measurements and helps determine transcatheter indication, the agreement of these techniques have not been systemically evaluated in dogs.

Objective/Hypothesis: The objective of this study was to describe agreement between Doppler echocardiographic methods of transpulmonary pressure gradient estimation and peak-to-peak pressure gradient at catheterization (PGcath) in dogs. We hypothesized that with reference to PGcath, mean echocardiographic PG (PGecho-mean) would have less bias than peak modal instantaneous echocardiographic PG (PGecho-peak).

Animals: Dogs with congenital PS that underwent BPV at one of two teaching hospitals.

Methods: Cases that underwent echocardiography and subsequent BVP separated by <30 days were retrospectively identified. For each echocardiogram, measurements from Doppler recordings were used to determine average PGecho-mean and PGecho-peak from 3–5 consecutive beats. Peak-right-ventricular-to-peak-pulmonary-artery pressure gradients (PGcath) were obtained from catheterization reports. Bland-Altman analysis was used to assess agreement between echocardiographic and catheterization data.

Results: Data from 205 cases were evaluated. Relative to PGcath, bias (95% limits of agreement) for PGecho-mean and PGecho-peak were −19.9 mm Hg (−93.9 to 54.0 mm Hg) and 37.92 mm Hg (−39.8 to 115.7 mm Hg), respectively. Proportional bias, greater at higher gradients, was observed for both methods.

Conclusions and Clinical Importance: On average, PGecho-mean and PGecho-peak under- and over-estimated PGcath, respectively, with wide limits of agreement for both. Over-reliance on echocardiographic PG for assessment of PS severity might be problematic.

¹School of Veterinary Medicine, University of California-Davis, Davis, CA, USA; ²TriviumVet, Waterford, Ireland; ³University of Arizona, Tucson, AZ, USA; ⁴Associate Dean and Professor of Cardiology, Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California-Davis, Davis, CA, USA

Background: Therapies to treat and prevent feline hypertrophic cardiomyopathy (HCM) are lacking. The mammalian target of rapamycin (mTOR) is a master regulator of cell growth, metabolism, and protein synthesis, and represents a therapeutic target for HCM. A recent clinical trial demonstrated that mTOR inhibition via chronic delayed-release (DR) rapamycin administration halts progression of left ventricular wall thickness with no adverse events or clinical pathology derangements, however, molecular effects of rapamycin in cats with HCM remain unknown.

Hypothesis/Objectives: This study aimed to characterize the multiomic effects of weekly low- and high-dose, oral, DR rapamycin in HCM-affected colony cats via RNA-sequencing and proteomic profiling. We further aimed to assess clinicopathologic, cardiac biomarker, and histopathologic responses to therapy.

Animals: Twelve purpose-bred cats were studied (3 low-dose HCM+, 3 high-dose HCM+, 3 untreated HCM+, and 3 untreated control).

Methods: Plasma and urine samples were obtained at day 0 and 56 of DR rapamycin dosing. Tissue samples (left ventricular posterior wall and interventricular septum) were obtained at necropsy on day 60. RNA-sequencing was performed on all tissues and LC-MS profiling was performed on day 0 and 56 plasma and urine and day 60 tissues.

Results: Differential transcript and relative protein expression analyses revealed intrinsic molecular effects between and within treatment groups with no safety or tolerability concerns identified via clinical pathology.

Conclusions and Clinical Importance: Results highlight pathways impacted in HCM-affected cats receiving oral DR rapamycin and provide key insights into multiomic differences observed in disease.

¹QTest Labs, Columbus, OH, USA; ²Vetcare; ³Dechra

Background: Zenalpha (medetomidine-vatinoxan) is a sedative-analgesic for dogs containing the novel molecule, vatinoxan, which counteracts medetomidine's cardiovascular depressive effects. To date, the use of Zenalpha has been investigated in healthy dogs and its safe use in cardiac patients is to be determined.

Hypothesis/Objectives: The objective was to compare the cardiovascular effects of Zenalpha to dexmedetomidine in dogs with mild to moderate heart failure.

Animals: Seven purpose-bred, tachy-paced Beagles with ejection fraction of 45 ± 5% including mild concomitant left-ventricular enlargement.

Methods: In this blinded crossover study each dog received Zenalpha (0.25 mg/m² medetomidine and 5 mg/m² vatinoxan) or dexmedetomidine (0.25 mg/m²) intramuscularly. Heart rate (HR), ECG and mean arterial pressure (MAP) were recorded and cardiac output measured at intervals until 120 min post-treatment. Differences between treatments and baseline were evaluated with repeated measures analysis (P < 0.05).

Results: Compared to dexmedetomidine stroke volume (SVI) and cardiac indices (CI) were significantly higher with Zenalpha until 60- and 120-min post-treatment, respectively. SVI did not decrease significantly from baseline with Zenalpha. CI and HR decreased significantly from baseline with both treatments. With Zenalpha CI and HR returned to baseline at 120 and 90 min, respectively, and HR was significantly higher than with dexmedetomidine at 90- and 120-min post-treatment. Compared to dexmedetomidine MAP was significantly lower from 15 to 90 min post-treatment with Zenalpha remaining below baseline until 120 min.

Conclusions and Clinical Importance: In comparison to dexmedetomidine Zenalpha caused less detrimental cardiovascular changes in dogs with mild to moderate heart failure.

¹Tel Aviv University, Tel Aviv-Yafo, Israel; ²Ben-Gurion University of the Negev, Be’er Sheva, Israel

The Ca 2+ -activated SK4 K+ channel is gated by Ca 2+ -calmodulin (CaM) and is expressed in immune cells, brain, and heart. A cryo-EM structure of the human SK4 K+ channel recently revealed four CaM molecules per channel tetramer, where the apo CaM C-lobe and the holo CaM N-lobe interact with the proximal C-terminus and the linker S4-S5, respectively, to gate the channel. Here, we show that phosphatidylinositol 4–5 bisphosphate (PIP2) potently activates SK4 channels by docking to the boundary of the CaM binding domain. A novel allosteric blocker, BA6b9, was designed to act to the calmodulin-PIP2 binding domain, a previously untargeted region of SK4 channels, at the interface of the proximal C-terminus and the linker S4-S5. Molecular docking and patch-clamp electrophysiology indicate that BA6b9 inhibits SK4 channels by interacting with two specific residues, Arg191 and His192 in the linker S4-S5, not conserved in SK1-SK3 subunits, thereby conferring selectivity and preventing the Ca 2+ -CaM N-lobe to properly interact with the channel linker region. Immunohistochemistry of the SK4 channel protein in rat hearts showed a widespread expression in the sarcolemma of atrial myocytes, with a sarcomeric striated Z-band pattern, and a weaker occurrence in the ventricle but a marked incidence at the intercalated discs. BA6b9 significantly prolonged atrial and atrioventricular effective refractory periods in rat isolated hearts and reduced atrial fibrillation induction ex vivo. Our work suggests that inhibition of SK4 K+ channels by targeting drugs to the calmodulin-PIP2 binding domain provides a promising anti-arrhythmic therapy.

JASMINE Veterinary Cardiovascular Medical Center

Background: Mitral valve repair (MVR) could be a curative treatment for myxomatous mitral valve disease (MMVD) in dogs. However, the optimal timing for surgery is not known. Mitral insufficiency echocardiographic (MINE) score is an easy-to-use echocardiographic based classification used to assess the severity of MMVD in dogs for medical treatment.

Hypothesis/Objectives: We hypothesized that the MINE score can be used for estimating the outcome of MVR.

Animals: We retrospectively analyzed the data of dogs with MMVD that underwent MVR at our institute from February 2017 to December 2020. We excluded cases that did not have enough data required for calculating the MINE score.

Methods: Echocardiographic variables were used to classify the cases into four stages preoperatively using the MINE scoring system: mild (score: 4–5), moderate (score: 6–7), severe (score: 8–12), and late (score: 13–14). Thoracic radiographs and echocardiography were evaluated in the preoperative period, 6- and 12-months post-surgery.

Results: The study included 897 dogs (mild = 16, moderate = 121, severe = 679, late = 81). The higher the disease stage, the larger the heart size both pre- and post-surgery. The four groups did not have difference in two-year survival rate for all-cause mortality derived by Kaplan-Meier curve: 92%, 77%, 85%, and 87%, respectively (P = 0.52; Log-rank test).

Conclusions and Clinical Importance: The MINE score can be used to predict the extent of cardiac reverse remodeling. However, it is unrelated to postoperative mortality. Therefore, estimating surgical outcomes require comprehensive factors, including clinical signs, arrhythmia, and medications.

¹University of Florida, Gainesville, FL, USA; ²Assistant Professor, Small Animal Clinical Sciences, University of Florida, Gainesville, FL, USA; ³Clinical Professor, Small Animal Clinical Sciences, University of Florida, Gainesville, FL, USA

Background: Heart failure-associated hypochoremia can be depletional or dilutional from free water retention. Serum osmolality reflects free water, but has not been evaluated in dogs with heart disease.

Hypothesis/Objectives: To determine if serum osmolality is related to heart disease stage and the amount of mathematical correction of serum chloride (Cl-) concentrations in healthy dogs and dogs with myxomatous mitral valve degeneration (MMVD).

Animals: Seventy-seven dogs (20 healthy, 25 Stage B MMVD, 32 Stage C/D MMVD).

Methods: Serum Cl- was mathematically corrected. Osmolality was calculated (cOsm) and directly measured by freezing point depression (dmOsm) and compared by Bland-Altman analysis. Biochemical variables and osmolarity were compared among healthy, Stage B and Stage C/D dogs. Correlations were explored between osmolality and biochemical variables. Median and IQR are presented and P < 0.05 was considered significant.

Results: The cOsm was different among groups (P = 0.003), with Stage B (310 mOsm/kg; 306, 316) and C/D dogs (312 mOsm/kg; 308, 319) having higher cOsm than healthy dogs (305 mOsm/kg; 302, 308). Osmolality methods were moderately correlated (P < 0.0001, r = 0.46) but with proportional bias and poor agreement. The amount of Cl- correction was negatively correlated with cOsm (P < 0.0001, r = −0.78) and dmOsm (P = 0.004, r = −0.33). Serum bicarbonate was negatively correlated with Cl- (P < 0.0001, r = −0.67).

Conclusions and Clinical Importance: Dogs with Stage B and Stage C/D heart disease had higher cOsm than healthy dogs. Osmolality was inversely related to the amount of Cl- correction which supports its use in the assessment of relative free water. Poor agreement between cOsm and dmOsm prevents methodological interchange.

¹BON Animal Medical Center, Suwon, Republic of Korea; ²Jeonbuk National University, Jeonju, Republic of Korea

Background: The current diagnostic recommendations for Dirofilaria immitis (D. immitis) infection in dogs rely on detecting antigens primarily produced by adult females, combined with microfilariae (mf) detection tests.

Hypothesis/Objectives: This study aims to compare LAMP PCR and the Modified Knott's (MK) test for mf detection, used in conjunction with antigen detection tests, to screen for canine heartworm infection in shelter dogs.

Animals: Matched whole blood samples were collected from 35 shelter dogs in Gunsan, Jeollabukdo (Republic of Korea), between June and October 2022. The study was approved by the Institutional Animal Care and Use Committee (IACUC).

Methods: Blood samples were analyzed for the presence of mf using the MK test and for D. immitis DNA using a species-specific LAMP PCR.

Results: Among the 10 antigen kit-positive animals, 4 (11.4%; 4/35) were found to have microfilariae morphologically identified as D. immitis. In comparison, LAMP PCR detected D. immitis DNA in two additional heartworm-positive samples, accounting for 17.1% (6/35).

Conclusion and Clinical Importance: Although LAMP PCR was not statistically significant compared to the MK test, it detected a greater number of D. immitis cases and showed more consistency with the results of antigen detection tests. In clinical use, LAMP PCR offers advantages over the MK test, as it does not require a microscope and can be easily employed with any blood sample, similar to advanced antigen test kits, regardless of observer subjectivity. Consequently, in conjunction with antigen testing, LAMP PCR could serve as an essential screening test for D. immitis infection in canine populations.

Laboratory of Veterinary Internal Medicine, Veterinary Teaching Hospital, Chungbuk National University, Cheongju, Republic of Korea

Background: Angiopoietin (Ang) plays a key role in regulating vascular integrity. Ang-2 is considered a potential biomarker for cardiovascular diseases in humans.

Objectives: To evaluate the relationships between the severity of MMVD and serum Ang-1 and Ang-2 concentrations and between PH probability and serum Ang-1 and Ang-2 concentrations in dogs with MMVD.

Animals: Seventy-four dogs (control, n = 12; MMVD, n = 62) were included in this study.

Methods: We retrospectively reviewed the medical data of dogs diagnosed with MMVD at our institution between July 2018 and June 2022. The serum Ang-1 concentration was analyzed using a commercial canine-specific ELISA kit. Serum Ang-2 concentration was analyzed using a commercial Human ELISA test kit and validated for use in dogs.

Results: The median serum Ang-1 concentration did not differ among the study groups. The median serum Ang-2 concentration was significantly higher in dogs with stage B2 MMVD (P = 0.022) and acute CHF (P = 0.001) than in control dogs. In addition, the mean serum Ang-2 concentration was significantly higher in dogs with high PH probability than in those with a low probability (P < 0.001) and intermediate PH probability (P = 0.001).

Conclusions and Clinical Importance: Circulating Ang-2 levels significantly increase in dogs with advanced MMVD and high PH probability, suggesting that Ang-2 may play a role in endothelial dysfunction in dogs with advanced heart disease.

Figure 1

Figure 2

Figure 3

Figure 4

¹Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA; ²College of Veterinary Medicine, University of Florida, Gainesville, FL, USA

Background: Diet-associated DCM can occur in dogs eating non-traditional diets (NTDs) high in pulses, but these diets also have been associated with changes in the erythron. Healthy laboratory dogs eating a high pea/lentil diet for one month had significant decreases in red blood cell count (RBC), hematocrit, and hemoglobin (Bakke et al 2022). Decreases in RBC also were seen in two other studies in healthy dogs eating high pulse diets (Quilliam et al 2021; Reis et al 2021), but the cause is unknown.

Hypothesis/Objectives: To compare red blood cell morphologic parameters and indices between dogs with DCM eating NTDs or TDs.

Animals: Forty-six dogs with DCM: 38 eating NTDs (pulses in the top ten ingredients) and 8 eating TDs (no pulses in the top ten ingredients).

Methods: RBC parameters were recorded from a complete blood count from the time of DCM diagnosis. A board-certified veterinary clinical pathologist (FC) blinded to dogs’ diets evaluated RBC indices. Variables were compared between diet groups using chi-square and Mann-Whitney U tests.

Results: RBC number (P = 0.72), hematocrit (P = 0.63), and hemoglobin (P = 0.59) were not significantly different between diet groups. However, red blood cell distribution width (RDW) was significantly lower in dogs eating NTDs compared to TDs (P = 0.01). Some RBC indices were more prevalent in the NTD group (e.g., poikilocytes, echinocytes, keratocytes, elliptocytes, and eccentrocytes), although none reached statistical significance.

Conclusions and Clinical Importance: RBC indices and lower RDW in dogs eating NTDs may provide clues to pathogenesis of diet-associated DCM.

¹Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA; ²Professor, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA; ³CVCA Cardiac Care for Pets; ⁴Irish Wolfhound Foundation

Background: Apparently healthy dogs eating non-traditional diets (NTDs) have larger left ventricular diameter, lower systolic function, and more ventricular premature complexes (VPCs) compared to dogs eating traditional diets (TDs). It is unknown whether this finding also occurs in Irish Wolfhounds.

Hypothesis/Objectives: To compare electrocardiographic and echocardiographic findings between Irish Wolfhounds eating NTDs and TDs.

Animals: Irish Wolfhounds that had echocardiography performed at dog shows between 2018–2020.

Methods: Demographic information, echocardiographic measurements, cardiac rhythm (from a rhythm strip), and main diet (i.e., the diet providing each dog's main source of calories) were recorded. Diets were classified as NTDs if the diet contained any pulses in the top ten ingredients and as TDs if there were no pulses in the top ten ingredients.

Results: One hundred forty-eight Irish Wolfhounds had echocardiograms performed during this time period. Dogs were excluded because of pre-existing heart disease (n = 12), raw or homemade diet (n = 28), and unknown diet (n = 9). Of the 96 eligible dogs, 35 were eating NTDs (median pulse score = 42 [range, 16–104]) and 61 were eating TDs (median pulse score = 0 [range, 0–11]; P < 0.001). There was no significant difference in age, sex, or body condition score. There were no significant differences in echocardiographic measurements between the two diet groups. However, 6/35 dogs eating NTDs (17%) had VPCs compared to 1/61 dogs eating TDs (2%; P = 0.009).

Conclusions and Clinical Importance: Similar to a previous study of four dog breeds, Irish Wolfhounds eating NTDs had significantly more VPCs compared to dogs eating TDs.

Laboratory of Veterinary Internal Medicine, College of Veterinary Medicine, Chungbuk National University, Cheongju, Republic of Korea

Background: In human, neutrophilia is linked to the development of acute heart failure, and lymphopenia is associated with poor prognosis. The neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), and platelet-to-lymphocyte ratio (PLR) are newly proposed inflammatory biomarkers. As MMVD is the most common acquired heart disease in dogs, evaluation of inflammatory biomarkers is needed.

Objectives: To investigate NLR, MLR, and PLR in dogs with MMVD.

Animals: In total, 106 dogs with MMVD and 22 healthy dogs were included in the study.

Methods: Complete blood count data were obtained retrospectively, and NLR, MLR, and PLR were compared between dogs with MMVD and healthy dogs.

Results: NLR and MLR were significantly higher in dogs with MMVD C and D (NLR of 4.99 [3.69–7.27]; MLR of 0.56 [0.36–0.74]) than in healthy dogs (NLR: 3.05 [1.82–3.37], P < 0.001; MLR: 0.21 [0.14–0.32], P < 0.001), MMVD stage B1 (NLR: 3.15 [2.15–3.86], P < 0.001; MLR: 0.26 [0.20–0.36], P < 0.001), and MMVD stage B2 dogs (NLR: 3.22 [2.45–3.85], P < 0.001; MLR: 0.30 [0.19–0.37], P < 0.001). The area under the receiver operating characteristic curves of the NLR and MLR to distinguish dogs with MMVD C and D from those with MMVD B were 0.84 and 0.89, respectively. The optimal cutoff value for NLR was 4.296 (sensitivity, 68%; specificity, 83.95%), and the MLR value was 0.322 (sensitivity, 96%; specificity, 66.67%).

Conclusions and Clinical Importance: NLR and MLR can be used as adjunctive indicators of CHF in dogs.

Animal Medical Center, Jeonbuk National University, Jeonju, Republic of Korea

Background: According to a study conducted in the United States, myxomatous mitral valve disease (MMVD) is the most common acquired cardiovascular disease in dogs. It can be suspected by cardiac murmur or chest radiography, and the golden standard for diagnosis is evaluation of cardiac morphologic changes by echocardiography.

Hypothesis/Objectives: To identify the diagnostic value of pulmonary vein to pulmonary artery ratio (PA/PV) measurement with echocardiography for dogs diagnosed as MMVD.

Animals: A total of 75 client-owned dogs who visited Jeonbuk National University Animal Medical Center from October 2020 and October 2022 were retrospectively studied.

It was approved by IACUC.

Methods: The PA/PV was measured using bi-dimensional mode in the right parasternal long axis four chamber view.

Results: The PV/PA in each group: control (1.08 ± 0.22), stage B1 (1.32 ± 0.30), stage B2 (2.06 ± 0.72), stage C (2.94 ± 1.01). Using One-way ANOVA analysis, it was confirmed that the PV/PA increased significantly as the MMVD stage progressed (P < 0.001). Additionally, PV/PA was higher in the congested heart failure (CHF) group when compared with the no-CHF group (P < 0.001).

Conclusion and Clinical Importance: In conclusion, as the severity of MMVD increased, PV/PA significantly increased, and it was confirmed that there was a positive correlation with conventional indicators. The PV/PA measurement has advantages of being easy and simple to evaluate compared to existing echocardiography indices. However, additional studies with various variables controlled are required, and more data should be accumulated to support the reliability of the study.

JASMINE Veterinary Cardiovascular Medical Center

Background: Myocardial protection techniques in open-heart surgery have yet to be well-researched and standardized in veterinary medicine. Recently, del-Nido cardioplegia has been reported as a new technique in humans.

Hypothesis/Objectives: This prospective study aimed to compare the utility of del-Nido cardioplegia with the conventional technique for mitral valve repair (MVR) in dogs and assessed myocardial damage using cardiac troponin-I (cTnI).

Animals: Forty client-owned dogs eligible for MVR were randomly divided into Group C (conventional technique) and Group D (del-Nido). Consent for the study was obtained from owners beforehand.

Methods: Group C used St. Thomas solution with 50% blood and potassium (40–50 mEq/L) every 10 min. Group D used the del-Nido cardioplegic technique, administered once or only when required, containing 20% blood, lidocaine (125 mg/L), and potassium (30 mEq/L). The levels of cTnI were assessed four times (before surgery and 2, 12, and 24 h after surgery).

Results: There were no differences between the two groups regarding operative time, cardiopulmonary bypass time, or aortic cross-clamping time during the procedure. However, the time from declamping to the return of sinus rhythm was shorter in Group D. There were no significant differences in cTnI levels between the groups at any time.

Conclusions and Clinical Importance: In conclusion, both techniques in this study facilitated the safe performance of MVR: the lack of a difference in cTnI levels after surgery indicates that postoperative myocardial damage was comparable. However, the patients with del-Nido cardioplegia had a smoother resumption of sinus rhythm following surgery.

¹College of Veterinary Medicine, University of Missouri, Columbia, MO, USA; ²Associate Professor, Veterinary Pathobiology, College of Veterinary Medicine, University of Missouri, Columbia, MO, USA; ³Graduate, Veterinary Pathobiology, College of Veterinary Medicine, University of Missouri, Columbia, MO, USA; ⁴Adjunct Professor, Veterinary Diagnostics Laboratory, College of Veterinary Medicine, University of Missouri, Columbia, MO, USA; ⁵Associate Professor, Cardiology, College of Veterinary Medicine, University of Missouri, Columbia, MO, USA

Background: Mucopolysaccharidoses (MPS) are a collection of heritable lysosomal storage disorders that result in multi-systemic dysfunction including cardiac disease. The most severe form (MPS1 or Hurler's syndrome) is due to deficiencies in the alpha-L-iduronidase enzyme.

Hypothesis/Objectives: To describe the clinical cardiac features in a family of Basset hounds and to identify the causal mutation.

Animals: Three related Basset hounds with suspected MPS and DNA samples from 740 individual Basset hounds.

Methods: Echocardiography, electrocardiography, and post-mortem evaluations were performed in the clinically affected dogs. Whole genome sequencing was performed from a related dog with compatible clinical signs and a positive toluidine urine spot test for MPS. DNA samples from both related and unrelated Basset hounds were genotyped for the likely causal sequence variant with an allelic discrimination assay.

Results: Affected dogs had varying degrees of mitral, tricuspid, and aortic valvular thickening and regurgitation as well as aortic root dilation. No arrhythmias or conduction disturbances were noted. Histopathology confirmed excessive glycosaminoglycan accumulation within the cardiac valves. Whole genome sequencing revealed a rare, but likely causal homozygous glycine-to-serine missense mutation in IDUA. To date, genotyping has revealed 13 DNA samples homozygous for the variant allele (including the clinically affected dogs), 50 were heterozygous, and 677 tested homozygous for the reference allele. The variant allele frequency was 5.6% for the genotyped cohort.

Conclusions and Clinical Importance: A novel IDUA variant is associated with the development of classical cardiac signs of MPS1 in Basset hounds and genetic testing may help guide breeding decisions.

Belij Klyk

Pulmonary hypertension is a complex syndrome that affects pulmonary circulation and the right heart. This syndrome progression is a prognosis-worsening factor and is associated with decreased survival and low quality of living. Conventional treatment includes phosphodiesterase 5 inhibitors (sildenafil or tadalafil) and combined drugs such as pimobendan (phosphodiesterase 3 inhibitor). In the terminal stages, this treatment could be insufficient and cannot control all the symptoms.

In this study, we retrospectively analyzed patients with severe pulmonary hypertension and additional treatment with bosentan (endothelin-1 inhibitor) which is believed to improve prognosis and outcome in diseased dogs.

We studied 23 client-owned dogs with refractory pulmonary hypertension of different etiology, already treated with sildenafil and with symptoms of dyspnea, syncope, ascites, and weakness. The diagnosis was based on the EchoCG studies and disease history analysis, according to ACVIM consensus statements in pulmonary hypertension. In order to determine the efficacy of bosentan, based on its extended impact and laboratory data in animals, we divided patients into two groups: 1—dogs treated for less than two weeks (n = 9), 2—dogs treated for a longer period (n = 14).

Results: The 2nd group had significant improvements in ascites (9/14), dyspnea (14/14), syncope (13/14), activity (10/14). Median survival time in the 1st group was 5 days, in the 2nd—5 months. EchoCG showed a positive trend in TAPSE, pulmonary vein to right pulmonary artery ratio, and right pulmonary artery distensibility index, with a decrease in RV diameter and tricuspid regurgitation velocity after two weeks of treatment.

Conclusion: These findings show significant improvement in clinical and EchoCG parameters after bosentan treatment compared to previous sildenafil medication.

¹Small Animal Hospital, University of Florida, Gainesville, FL, USA; ²Clinical Assistant Professor, Cardiology, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA; ³Adjunct Professor, Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA

Background: The relative importance of vascular responses to pimobendan in dogs with congestive heart failure (CHF) are incompletely studied.

Hypothesis/Objectives: We hypothesized that if pimobendan reduces systemic vascular resistance, femoral arterial flow (estimated by Doppler velocity-time integral) will increase and arterial resistive index will decrease after a single dose of pimobendan in dogs with CHF.

Animals: Ten client-owned dogs with myxomatous mitral valve degeneration undergoing treatment for acute onset of CHF were studied.

Methods: Prospective, within-subjects study design. Duplex Doppler ultrasonography (DDU) was used to quantify femoral arterial volumetric flow and calculate resistive index at baseline and 2 h after a single oral dose of pimobendan (0.3 mg/kg). DDU recordings were measured offline by an operator blinded to treatment. Measurements pre-and post-pimobendan administration were compared using paired t-tests or Wilcoxon's signed-rank test.

Results: Mean dose (±SD) of furosemide at enrollment was 2.616 mg/kg (±1.56). Total VTI estimating flow over the cardiac cycle was unchanged from baseline to treatment (3.24 cm ± 1.82 vs. 3.24 cm ± 1.50). Resistive index at baseline (1.21 ± 0.16) was not different from pimobendan (1.30 ± 0.07, P = 0.105), although peak systolic velocity was 0.22 cm/s higher (P = 0.026) and minimal velocity 0.12 cm/s lower (P = 0.011) after pimobendan. Mean systolic blood pressure measurements were 126.5 mm Hg ± 20.13 and 131.0 mm Hg ± 19.97) pre- vs. post-pimobendan (P = 0.568).

Conclusion: A single dose of pimobendan following administration of furosemide did not produce measurable vasodilation or increased peripheral blood flow based on DDU in dogs with acute congestive heart failure.

Seoul National University, Seoul, Republic of Korea

Background: Myxomatous mitral valve disease (MMVD) is the most common cause of heart failure (HF) in dogs, and its risk assessment of HF is often challenging. Machine learning applied to electronic health records (EHRs) is an effective tool for predicting prognosis in the medical field.

Objectives: This study aimed to develop machine learning-based HF risk prediction models for dogs with MMVD using a dataset of EHRs.

Animals: A total of 143 dogs with MMVD between May 2018 and May 2022.

Methods: Complete medical records were reviewed for all patients. Demographic data, radiographic measurements, echocardiographic values, and laboratory results were obtained from the clinical database. Four machine learning algorithms (Random Forest, K-Nearest Neighbors, Naïve Bayes, Support Vector Machine) were used to develop the risk prediction models. Model performance was represented by plotting the receiver operating characteristic (ROC) curve and calculating the area under the curve (AUC). The best-performing model was chosen for the feature ranking process.

Results: Random forest showed superior performance to the other models (AUC = 0.88), while the performance of the K-nearest neighbors showed the lowest performance (AUC = 0.69). The top three models showed excellent performance (AUC ≥ 0.8). According to the random forest algorithm feature ranking, echocardiographic and radiographic variables had the highest predictive values for HF, followed by PCV and respiratory rates. Among the electrolyte variables, chloride had the highest predictive value for HF.

Conclusions and Clinical Importance: These machine-learning models will support clinical decision-making in estimating the prognosis of patients with MMVD.

¹Texas A&M University, College Station, TX, USA; ²Assistant Professor, Texas A&M University, College Station, TX, USA; ³Professor, Texas A&M University, College Station, TX, USA

Background: Prospective data reporting the prevalence of structural cardiac disease and heart murmurs in Borzoi dogs is lacking.

OBJECTIVE: To report echocardiographic findings and prevalence of heart murmurs in a cohort of healthy Borzoi.

Animals: 146 client-owned, clinically healthy, Borzoi.

Methods: Single center prospective cohort study. Auscultation and standard echocardiograms were performed by board-certified cardiologists. Longitudinal echocardiograms were performed in a subset.

Results: The population consisted of 86 females (58.9%) and 60 males (41.1%). Median age was 4 years (range 1.1–12.0). Heart murmurs were identified in 86/146 dogs (58.9%). Most Borzoi were structurally normal (119/146, 81.5%), with 64 normal dogs (43.8% of the total population) having an innocent heart murmur. Thirty-six structurally normal dogs had trace or mild mitral regurgitation (30.2% of normal dogs) and 43 had trace or mild tricuspid regurgitation (36.1% of normal dogs). Structural cardiac disease was identified in 21 dogs (14.4%), with another six dogs having equivocal diagnoses (4.1%). Dilated cardiomyopathy (DCM) was diagnosed in nine dogs (6.2%) and stage B1 myxomatous mitral valve disease (MMVD) was diagnosed in nine dogs (6.2%). Twenty-five dogs had longitudinal examinations. Two dogs developed occult DCM, two transitioned to an equivocal DCM diagnosis, and two developed stage B1 MMVD within two years. Two dogs with DCM (one occult, one equivocal) improved with diet change.

Conclusions and Clinical Importance: Structurally normal Borzoi commonly have trace or mild atrioventricular valve insufficiencies and innocent heart murmurs. All Borzoi with MMVD had normal heart size. Screening for DCM may be considered in the breed.

University of California Davis, Davis, CA, USA

Background: Furosemide, a commonly used diuretic, activates the circulating renin-angiotensin-aldosterone system (RAAS) in other species. Little is known about RAAS activation in horses.

Hypothesis/Objectives: We hypothesize that furosemide will cause transient elevation in both classical and alternative RAAS hormones.

Animals: Adult thoroughbreds from a university teaching herd were used for the cross over study design (n = 6) and baseline hormone levels (n = 8).

Methods: Horses received either intravenous furosemide (1 mg/kg) or saline. Circulating RAAS hormones were quantified at 0, 0.25, 0.5, 4, and 24 h post administration, via liquid chromatography-tandem mass spectrometry and/or equilibrium dialysis. Values were compared with a repeated measures mixed model. Paired protease inhibited samples were also analyzed and compared with Spearman's Correlation. Data are presented as median (baseline) or difference in mean (elevation), [95% CI].

Results: Only angiotensin-II (7.4 [4.8–10.7] pMol/L) was consistently above the limit of quantification at baseline. Furosemide resulted in an increase in angiotensin I (8.0 [1.04–15.03] pMol/L, P = 0.02), angiotensin-II (33.7 [10.0–57.4] pMol/L, P = 0.002), angiotensin-IV (2.0 [0.64–3.39] pMol/L, P = 0.001), angiotensin 1–5 (5.6 [1.84–9.32] pMol/L, P = 0.0009), and aldosterone (180.8 [3.1–358.5] P = 0.04) compared to saline at 4 . Correlation between protease inhibition and equilibrium dialysis was high for Angiotensin-I and Angiotensin II (r = 0.81 and 0.86, respectively; P < 0.0001).

Conclusions and Clinical Importance: Baseline levels of circulating RAAS hormones are low in healthy horses. Furosemide produced an increase in hormones associated with both the classical and alternative RAAS pathways. Comprehensive RAAS data offers a model to study pharmacologic and pathologic activation in horses.

¹University of Guelph, Guelph, ON, Canada; ²Myant, Inc., Etobicoke, ON, Canada

Background: Smart textiles have been developed to replace standard adhesive electrodes for collection of electrocardiograms, though limited work has assessed their potential in equine medicine.

Hypothesis/Objectives: The objective of this study was to assess the validity of a smart textile ECG device for long-duration heart rate variability (HRV) assessment.

Animals: Four healthy Warmblood horses.

Methods: ECGs were simultaneously recorded using a smart textile device and a standard telemetric device from unrestrained horses for 6 hrs in a controlled pilot study. Data were analyzed to calculate heart rate and HRV metrics [average RR intervals, the axial and perpendicular dispersions from the line of identity from the Poincaré plot (SD1 and SD2, respectively), root mean square of successive differences (RMSSD), percentage of successive RR interval differences (pNN50), and oscillations in the very-low frequency (VLF), low-frequency (LF), and high-frequency (HF) bands]. Data were compared using Bland-Altman analysis and Pearson coefficients.

Results: Excellent agreement with small biases were observed between the two devices and perfect correlations (r = 1.0, P < 0.0001) were found for all metrics except for VLF and HF. Bland-Altman tests revealed a mean bias of 0.003 bpm (95% limits of agreement: −0.06 to 0.06) for HR, −0.05 ms (−2.62 to 2.52) for RR intervals, −0.30 ms (−3.60 to 3.00) and −1.10 ms (−5.49 to 3.29) for SD1 and SD2, respectively, and −0.43 ms (−5.09 to 4.23) for RMSSD.

Conclusions and Clinical Importance: This study demonstrates that a smart textile device is a practical alternative for long-duration assessment of HRV in resting horses.

¹University of Adelaide; ²University of Copenhagen, Copenhagen, Denmark; ³Baker Heart and Diabetes Institute, Melbourne, VIC, Australia; ⁴University of Melbourne, Melbourne, VIC, Australia

Background: Athletic horses have a high prevalence of cardiac arrhythmia in the absence of structural heart disease. The underlying triggers and substrate for arrhythmia in this species are not well studied.

Hypothesis: Thoroughbred racehorses will have myocardial fibrosis, increased myocyte diameter, and a greater density of fibroblasts compared to untrained horses.

Animals: Thoroughbred racehorses, comprising 15 that died from sudden cardiac death (SCD) and 18 that died from other fatal injuries (OFI), were compared to 10 healthy untrained (UT) wild horses.

Methods: Cardiac tissues were sampled during post-mortem. OFI and UT were age matched to the SCD group. Two atrial and three ventricular sites were stained with Sirius red for assessment of myocardial fibrosis and triple antibody stain (WGA, vimentin, and GS-IB4) for myocyte diameter and fibroblast density. Measurements were made by a blinded operator using automated analysis with commercial software. Results were tested for normality using the Shapiro-Wilk test and differences assessed with one-way ANOVA with multiple comparisons.

Results: SCD had a greater fibrosis proportion compared to UT at 4/5 examined sites. UT had reduced myocyte diameter at 5/5 sites compared to SCD or OFI. There were no significant differences between SCD and OFI for either fibrosis proportion or myocyte diameter and there were no differences between any group for fibroblast density.

Conclusions and Clinical Importance: Thoroughbred racehorses have histological myocardial hypertrophy. Myocardial fibrosis is pronounced in SCD, and this could be a substrate for arrhythmia. The absence of increased fibroblast density might suggest underlying chronic fibrotic remodeling.

¹University of Pennsylvania, Philadelphia, PA, USA; ²Sports Medicine Practice

Background: Exercising arrhythmias can cause poor performance or sudden death.

Hypothesis/Objectives: To describe the association of exercising arrhythmias in field recordings with type, intensity and duration of exercise and presence of previous cardiac signs.

Animals: Cohort study of 36 Eventing horses in active competition.

Methods: 571 recordings [median (IQR), 7(4–12) ECGs/horse] were evaluated and 167 were <95% readable and discarded. Mixed-effects logistic regression tested the association of the dichotomous outcomes presence of arrhythmia (arrhythmia) and presence of complex arrhythmia (arrhyhmiacomplex). Duration of recording (mins) (duration), average heart rate (beats/min) (HRaverage) and peak heart rate (beats/min) (HRpeak) were set as the fixed effects. Analysis was confounded by exercise type and prior cardiac signs (horses enrolled after referral for cardiac evaluation) with horse ID as the random effect. Mixed-effects Poisson regression analyzed number of premature complexes (nPC) analogously.

Results: There was arrhythmia in 33.2% of the recordings, arrhyhmiacomplex in 5.7% and the n°PC was 0(0–1) [range 0–99 PC/ECG]. 32.7% of the recordings were gallops, 23.8% flat sessions, 16.3% hacks, 15.1% jumping sessions, 5.2% cross-county schooling sessions, 4.7% trotting sessions and 2.2% cross-country competition. HRpeak was (mean ± SD) 169 ± 35 and HRaverage 94 ± 19. Increased likelihood of arrhythmia was associated with duration (OR = 1.022, CI [1.004, 1.041], P = 0.017) and HRpeak (OR = 1.037, CI [1.019, 1.055], P < 0.001. Risk of arrhyhmiacomplex was increased with HRpeak (OR = 1.040, CI [1.017, 1.064], P = 0.001) and cardiac signs (OR = 6.157, CI [1.390, 27.270], P = 0.017). Increased n°PC was associated with duration (IRR = 1.013, CI [1.009, 1.017], P = <0.001), HRaverage (IRR = 1.033, CI [1.027, 1.041], P < 0.001) and hacks (IRR = 2.44, CI [1.079, 5.539], P = 0.0320). None of the horses developed cardiac signs during the study.

Conclusions and Clinical Importance: Intensity, duration, type of exercise and previous cardiac signs are relevant when evaluating exercising ECGs in Eventers.

University of Pennsylvania

Background: Methods to determine thresholds that separate different exercise intensities often require equipment and the involvement of a veterinarian. Detrended fluctuation analysis (DFA) is a heart rate variability metric that quantifies the degree of correlation within a heart rate series and has been proposed as a non-invasive way of assessing cardiac parasympathetic activity during exercise. The main advantage of DFA is the potential to provide real time or retrospective information under field conditions using rider friendly wearable monitors and its potential association with exercise intensity thresholds and fatigue.

Objectives: The objective of this study was to 1—describe the behavior of the first component of DFA (DFA-α1) during standardized field incremental exercise tests. 2—determine if DFA-α1 is associated with lactate concentrations in this setting. We hypothesized that DFA-α1 would have a high correlation with lactate measurements and that this association would be stronger than the association with heart rate and speed.

Animals: 33 competitive Eventing horses and sport horses without competitive goals.

Methods: In vivo observational study that analyzed exercising electrocardiograms obtained in 60 standardized exercise tests in the field.

Results: DFA-α1 was significantly associated with lactate levels (ρ = −0.49, P < 0.001) but the association was weak. A stronger association was observed between lactate and speed (ρ = −0.80, P < 0.001), as well as lactate and heart rate (ρ = 0.74, P < 0.001).

Conclusions: DFA-α1 association with lactate does not support its use as a surrogate of lactate in field incremental standardized tests used for sport horses.

¹Vetsuisse Faculty, University of Zurich, Zurich, Switzerland; ²Director, Clinic for Equine Internal Medicine, Clinic for Equine Internal Medicine, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland

Background: Cardiac murmurs caused by mitral (MR) or aortic regurgitation (AR) in horses often prompt further diagnostics to assess disease severity and prognosis.

Hypothesis/Objectives: This study aimed to examine the use of Audicor Acoustic Cardiography to detect murmurs and quantify cardiac mechanical and hemodynamic function in horses with mild, moderate, or severe MR or AR.

Animals: 30 horses with MR, 18 with AR, 18 healthy horses.

Methods: Prospective study. The following variables were extracted from five consecutive, subsequently averaged 10-s snapshot analyses: heart rate (HR, min⁻¹), electromechanical activation time (EMAT, ms), HR-corrected EMAT (EMATc, %), left ventricular systolic time (LVST, ms), HR-corrected LVST (LVSTc, %), strength of third (S3) and fourth (S4) heart sound, and systolic dysfunction index (SDI, a function of QRS duration, QT interval, EMATc, and S3). Measurements were compared between groups using one-way ANOVA.

Results: Horses with AR were 6 (2–10) years [mean difference (95% CI of the difference of means)] older than horses with MR and 7 (2–12) years older than healthy horses. The LVST was 33 (5–60) ms shorter and the EMAT/LVST ratio 0.038 (0.001–0.075) higher in horses with MR compared to AR. Body weight, HR, EMAT, EMATc, LVSTc, strength of S3 and S4, and SDI were not significantly different between groups (P > 0.05).

Conclusions and Clinical Importance: Acoustic cardiography can detect differences in some systolic time intervals in horses with MR vs. AR. The clinical relevance as diagnostic point-of-care device in horses with MR or AR of various severity needs to be determined.

¹Equine Genetics and Genomics Lab, University of Minnesota, Minneapolis, MN, USA; ²University of Minnesota, Minneapolis, MN, USA; ³Associate Dean for Research and Professor of Equine Internal Medicine, University of Minnesota, Minneapolis, MN, USA; ⁴Assistant Professor of Genetics, Genomics, and Large Animal Internal Medicine, Veterinary Clinical Sciences, University of Minnesota, Minneapolis, MN, USA

Background: Echocardiography is a mainstay of cardiac evaluations. Numerous reference ranges have been published for different horse breeds, however, many were published >10 years ago. We are currently performing cardiac evaluations, including echocardiography, on 1,000 healthy Standardbred and Thoroughbred racehorses. In evaluating echocardiographic measurements, interobserver variability can be a significant source of data inaccuracy.

Objectives: Our primary objective is to identify structural cardiac abnormalities in and update reference ranges for healthy racehorses. Our secondary objective is to determine interobserver variability.

Animals: Echocardiography was performed on Thoroughbreds (n = 31) and Standardbreds (n = 53), comprised of 51 geldings, 24 mares, 4 stallions, and 5 undesignated, aged 2–10 years old.

Methods: This was a non-randomized observational case-control study. Echocardiography was performed on non-sedated horses. Standard measurements were obtained.

Results: Mean (standard deviation) values for Thoroughbreds and Standardbreds respectively were obtained: ejection fraction (64.37%, 4.92; 64.0%, 4.18), fractional shortening (37.35%, 3.82; 37.07%, 3.24), left atrial diameter (12.22 cm, 0.72; 12.42 cm, 0.77), interventricular septum (2.61 cm, 0.25; 2.65 cm, 0.33), diastolic left ventricular diameter (11.08 cm, 1.18; 11.25 cm, 1.08), left ventricular free wall (2.58 cm, 0.23; 2.32 cm, 0.25) and systolic left ventricular diameter (6.96 cm, 0.88; 7.08 cm, 0.76). No horses had clinically relevant structural disease.

Conclusions and Clinical Importance: These measurements will provide updated reference ranges for healthy racehorses and information about the proportion of horses with structural cardiac disease. Interobserver agreement will be evaluated for three observers.

¹Ghent University, Ghent, Belgium; ²Professor, Department of Internal Medicine, Reproduction and Population Medicine, Ghent University, Ghent, Belgium; ³Department of Internal Medicine, Reproduction and Population Medicine, Ghent University, Ghent, Belgium

Background: The most efficient treatment option for atrial fibrillation (AF) in horses is transvenous electrical cardioversion (TVEC) but the position of the electrodes during TVEC has been empirically determined.

Objective: To rationalize electrode positioning in horses during TVEC procedures by using finite element models (FEMs) to compare electric fields using different electrode configurations.

Animals: Scaled 3D heart model based on a CT scan of a healthy pony.

Methods: The FEMs were created by segmenting a CT scan into tissue compartments, followed by meshing and assigning tissue conductivities. The FEMs were modified during segmentation by adding 9 Fr 10 cm long TVEC catheter electrodes in different configurations during the segmentation stage. The electrical fields of different configurations with the positive and negative electrodes were calculated at different energy levels typically used by truncated biphasic exponential waveform defibrillators, as described in table 1. The relative efficacy and safety were calculated by determining the amount of atrial myocardium above the defibrillation threshold (5 V/cm) and at risk for potential tissue damage (>30 V/cm).

Results: Increasing the energy above 200 J only yields marginal improvements in defibrillation efficacy. Defibrillation between the middle of the right atrium and the coronary sinus resulted in the highest efficacy. Detailed results are given in table 1.

Conclusions and Clinical Importance: Using an in silico model improves our understanding of atrial fibrillation cardioversion in horses and may contribute to the development of alternative cardioversion techniques. It may be more beneficial to change the position of the catheters rather than increase the energy.

¹Ghent University; ²Department of Internal Medicine, Reproduction and Population Medicine, Ghent University; ³Department of Surgery and Anaesthesiology of Domestic Animals, Ghent University; ⁴Cardiology Department, AZ Maria Middelares

Background: Radiofrequency catheter ablation has been successfully applied to treat right atrial tachycardia in horses. Ablation of left-sided arrhythmias is complicated by the perilous retrograde arterial approach needed for left-sided catheterization. In human medicine, the left atrium is accessed femorally through transseptal puncture (TSP) of the fossa ovalis (FO). Recently a TSP technique via the jugular vein was developed for horses.

Hypothesis/Objective: To determine efficacy, complications and closure process of TSP in horses.

Animals: Three horses without cardiovascular disease, and two horses admitted for ablation of atrial fibrillation (AF).

Methods: Descriptive experimental study. TSP was performed under general anaesthesia by radiofrequency energy application on a guidewire to perforate the FO and allow advancement of a deflectable sheath under transthoracic and intracardiac echocardiographic (TTE and ICE) guidance. In three horses without cardiovascular disease, puncture closure was evaluated during four weeks by TTE and ICE.

Results: All TSPs were successful. Time from sheath positioning in front of the FO until successful transseptal access was 19–97 min. In two horses, balloon dilation of the puncture opening was needed for sheath advancement. Minor complications included transient atrial premature depolarisations (n = 1), self-terminating atrial tachycardia (n = 1) and self-terminating AF (n = 1) during radiofrequency energy application for puncture in the horses without pre-existing AF. Follow-up of the closure process (n = 3) using ICE showed closure 1–3 weeks after puncture.

Conclusions and Clinical Importance: TSP could be performed safely in horses using ICE guidance, which opens perspectives for management of left-sided atrial arrhythmias.

¹The University of Queensland, St Lucia, QLD, Australia; ²University of Georgia, Athens, GA, USA; ³The University of Melbourne, Parkville, VIC, Australia

Background: Leptin is an adipokine released from adipose tissue. There are inconsistent reports of associations between increased leptin concentrations with obesity and laminitis status in ponies.

Hypothesis/Objectives: Increased plasma leptin concentrations will be associated with obesity and laminitis in ponies.

Animals: Cross-sectional study of 211 Shetland and Welsh ponies sampled in Australia and the USA in autumn and/or spring.

Methods: Obesity was defined as a modified-Henneke body condition score >6/9. Laminitis was defined as a modified-Obel score >1/12. Plasma leptin concentrations were measured in all ponies by radioimmunoassay at Cornell University. Descriptive and interferential statistics were performed, with significance accepted at P < 0.05.

Results: Australian Welsh ponies had lower spring plasma leptin concentrations than American Welsh ponies (P = 0.0006). Compared to spring values, American Welsh ponies had lower autumnal plasma leptin concentrations (P = 0.01) while Australian Shetlands had higher autumnal plasma leptin concentrations (P = 0.004). Australian Welsh ponies had lower plasma leptin concentrations than Australian Shetlands in autumn (P = 0.009). Obese ponies (n = 122) had higher plasma leptin concentrations than non-obese ponies (n = 136, P < 0.0001). No difference in plasma leptin concentrations between laminitic (n = 50) and non-laminitic ponies (n = 120) were detected (P = 0.73).

Conclusions and Clinical Importance: Plasma leptin concentration is associated with obesity in ponies but varied with country, season, and breed, warranting careful interpretation of results. The clinical utility of measuring plasma leptin concentration in the diagnosis of laminitis remains to be determined.

¹College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA; ²The Ohio State University, Columbus, OH, USA; ³Associate Professor, Clinical Equine Internal Medicine, The Ohio State University, Columbus, OH, USA

Background: Glucocorticoids are frequently administered to horses, and this treatment is associated with risk of hyperinsulinemia-associated laminitis (HAL). Methods to predict development of treatment-associated HAL are needed.

Hypothesis/Objectives: Evaluate insulin and glucose dynamics before and after administration of dexamethasone (0.08 mg/kg PO q 24 h; DEX) and compare results between horses that subsequently developed laminitis (LAM) and those that did not (NONLAM) after a 14-day course of DEX administration. We hypothesized that insulin and glucose dynamics would differ between LAM and NONLAM horses.

Animals: 33 healthy adult horses were included.

Methods: Frequently-sampled insulin-modified IV glucose tolerance tests (FSIGTT) and oral sugar tests (OST) were performed at baseline and after 7 days of treatment with DEX. Minimal Model analysis was performed using FSIGTT data, and areas under the curve (AUC) of [insulin] (AUCins) and [glucose] (AUCg) were calculated from OST data. Paired Student's t-tests were used to compare LAM and NONLAM groups at baseline and after DEX.

Results: 5/33 horses (15.15%) developed clinical signs of laminitis during or shortly after the 14-day study period. AIRg (acute insulin response to glucose; P = 0.01) and AUCins (P = 0.002) were significantly higher in LAM versus NONLAM horses at baseline. Additionally, AUCins (P = 0.02) was significantly higher in LAM after DEX.

Conclusions and Clinical Importance: AIRg and AUCins calculated from the FSIGTT and OST, respectively, could predict development of HAL associated with glucocorticoid treatment and should be evaluated as biomarkers of this risk.

College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA

Background: Dietary management is the most important treatment for equine insulin dysregulation (ID) and often involves feeding low non-structural carbohydrate (NSC), high-protein ration balancers and grass hay. Data suggest that post-prandial hyperinsulinemia can be exacerbated by a high-protein meal in patients with ID, creating concern about the safety of this nutritional intervention.

Hypothesis: Consumption of a low-NSC, high-protein meal will induce post-prandial hyperinsulinemia, which will be amplified after induction of ID in horses.

Animals: Seven adult, light-breed horses with normal endogenous [ACTH].

Methods: Each horse underwent a frequently sampled insulin-modified IV glucose tolerance test to characterize systemic insulin and glucose dynamics, followed by a feed challenge test (1 kg ration balancer [min 32% crude protein, max 13% NSC] consumed within 15 min, with [insulin] and [glucose] measured at baseline and every 30 min for 240 min after the meal). Both tests were repeated after induction of ID (dexamethasone 0.08 mg/kg PO once daily for 7 days). Outcomes were compared between baseline and ID conditions.

Results: ID was associated with exacerbation of post-prandial hyperinsulinemia and hyperglycemia after high-protein meal feeding. ID AUCins (548.9 ± 150 μIU/mL×min) was significantly higher than baseline AUCins (216.2 ± 104.4 μIU/mL×min; P = 0.003). ID AUCgluc (89.5 [60−115] mg/dL×min) was significantly higher than baseline AUCgluc (75 [34.9−94] mg/dL×min; P = 0.03).

Conclusions and Clinical Importance: Horses with experimentally-induced ID displayed significantly higher glycemic and insulinemic responses to a high-protein meal than at baseline, suggesting that high-protein ration balancers may complicate nutritional management of equine ID.

¹Western College of Veterinary Medicine, University of Saskatchewan, SK, Canada; ²Prairie Diagnostic Services (PDS) Inc. and Western College of Veterinary Medicine, University of Saskatchewan, SK, Canada; ³Associate Professor, Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, SK, Canada

Background: Early diagnosis of equine metabolic syndrome (EMS) and pituitary pars intermedia dysfunction (PPID) is associated with increased survival and improved quality of life. Diagnosis includes measurement of adrenocorticotropic hormone (ACTH) and insulin concentrations for PPID and EMS, respectively.

Hypothesis/Objectives: To characterize the fluctuations in ACTH and insulin levels in healthy horses in Saskatchewan.

Animals: Study 1: Fifty-two (n = 52) client-owned horses. Inclusion criteria: no recent travel outside of Saskatchewan, normal physical exam findings, no history or evidence of ongoing illness.

Study 2: Eighty (n = 80) client-owned horses. Inclusion criteria: same as Study 1.

Methods: Study 1: Prospective, observational study. Blood samples were collected in spring and fall 2021, and ACTH and insulin concentrations were determined by chemiluminescence. Univariable and multivariable linear regression models were used.

Study 2: Prospective, observational study. Monthly sample collection started in July 2022 and will continue for a total of 12 months. Sample processing is the same as Study 1. Analysis will be performed with a generalized linear model.

Results: Study 1: ACTH and insulin levels increased in the fall compared to spring (P < 0.01). Age and fall ACTH levels were significantly associated (P = 0.005).

Study 2: Data collection is ongoing. Preliminary results will be available by June 2023.

Conclusions and Clinical Importance: Results so far highlight the seasonal trends in both ACTH and insulin levels in healthy horses in the Canadian prairies. These results will help characterize fluctuations in these biomarkers, in order to better understand their regional behavior and improve diagnostic accuracy.

¹University of Guelph, Guelph, ON, USA; ²The Ohio State University, Columbus, OH, USA

Background: Hyperglycemia is associated with mortality in horses. A key system in controlling glycemia and pancreatic function is the enteroinsular axis which consists of the incretin hormones glucagon-like peptide-1 (GLP-1), glucagon-like peptide-1 (GLP-2), and glucose-dependent insulinotropic polypeptide (GIP). Information on incretins in healthy and sick horses is lacking.

OBJECTIVE: Investigate the enteroinsular axis in healthy horses and horses with colitis and to determine their association with mortality.

Animals: 29 healthy horses and 91 horses with colitis (66 survivors, 24 non survivors).

Methods: Prospective case control study. Plasma insulin, glucose, GLP-1, and GIP concentrations were determined on admission. Data were analyzed by non-parametric methods and univariate analysis.

Results: Glucose was numerically, but not statistically, higher in non-surviving (n =23; 7.5 mg/dl, 4.8–9.5) than surviving (n = 63; 5.9 mg/dl, 5.3–7) horses with colitis (P = 0.05). GIP was significantly lower in horses with colitis (n = 93, median: 42 ng/ml, range: 31–90) than healthy (n = 29; 105 ng/ml, 50–165) horses (P = 0.01). GIP was lower in non-surviving (n = 24; 36 ng/ml, 17–53) than surviving (n = 66; 49 ng/ml, 33–97) horses with colitis (P = 0.01). Horses with colitis and low GIP were more likely to die or be euthanized (OR = 1.02, 95% CI = 1.002–1.036). GLP-1 was significantly higher in horses with colitis (n = 18, median: 48 ng/ml, range: 34–69) than healthy (n = 4; 22 ng/ml, 18–29) horses (P = 0.01).

Conclusions: Dysregulation of the enteroinsular axis occurred in horses with colitis. Hyperglycemia in non-surviving horses with colitis can be explained, at least in part, by impaired intestinal production of GIP.

¹Utrecht University, Utrecht, Netherlands; ²The University of Queensland, St. Lucia, QLD, Australia; ³Melbourne Veterinary School, The University of Melbourne, Melbourne, VIC, Australia

Background: The thyrotropin releasing hormone (TRH) stimulation test is used to diagnose pituitary pars intermedia dysfunction (PPID) by measuring ACTH concentration either 10- or 30-min post-TRH administration. Imprecise sampling time leads to significant ACTH variability in the 10-min protocol.

Hypothesis/Objectives: Determine if imprecise sampling time yields significant differences in ACTH concentrations using the 30-min protocol of the TRH stimulation test.

Animals: Twenty-seven horses >12 years, including 12 horses with PPID.

Methods: Blood was collected from each horse 0, 9, 10, 11, 29, 30 and 31 min after intravenous injection of 1 mg of TRH. ACTH concentrations were determined by chemiluminescent immunoassay. Differences in ACTH concentrations and variability in ACTH concentrations between protocols were analyzed with a one-way ANOVA and visualized with Bland-Altman plots. Significance was set at P < 0.05.

Results: Early or late sampling yielded a significant difference in ACTH concentrations using the 10-min protocol among all horses, the control horses but not those with PPID (P = 0.04, 0.01 and 0.37 respectively). There was no significant difference with the 30-min protocol in any group (P = 0.45, 0.21 and 0.63). No significant differences in the variability in ACTH concentrations between early or late sampling in either protocol detected in any group (P = 0.35, 0.24, 0.34, respectively).

Conclusions and Clinical Importance: The 30-min protocol of the TRH stimulation test is less affected by imprecise sampling and might be more useful in clinical settings. Precise timing during TRH stimulation tests remains fundamental for the diagnosis of PPID.

¹Queensland University of Technology, Brisbane City, QLD, Australia; ²Queensland University of Technology, Brisbane City, QLD, Australia; ³Professor, Queensland University of Technology, Brisbane City, QLD, Australia

Hypothesis/Objectives: Glucagon-like peptide-1 (GLP-1; encoded by the gene GCG) released from intestinal L-cells increases post-prandial insulin release. GLP-1 secretion has been examined in equine small intestine, but in other species L-cells are mainly located in the large intestine. The aim of this study was to determine large intestinal GLP-1 release in vitro. A second aim was to compare the sequence of GCG between healthy and insulin-dysregulated horses.

Animals: Tissue samples were sourced post-mortem from 10 horses at an abattoir. Genomic DNA was collected from 33 horses of varying metabolic status. Sample use was approved by an ethics committee.

Methods: Duplicate sections of cecum, ascending and descending colon were rinsed and placed in ice-cold phosphate-buffered saline prior to sectioning. Tissues were incubated for 60 min at 37°C in 1 mL Tyrode's buffer with Diprotin and 12 mM glucose. GLP-1 secretion was normalized to protein content and compared with one-way, repeated-measures ANOVA. Hybridised capture was used to generate a sequence for the exons of GCG in healthy and insulin-dysregulated horses and aligned against the reference genome.

Results: More GLP-1 was secreted from the ascending (66.7 ± 23.7 pM/mg; P = 0.01) and descending (62.9 ± 12.6 pM/mg; P = 0.006) colon, compared to cecum (9.59 ± 3.75 pM/mg). Sequences for GCG had 100% pairwise identity.

Conclusions and Clinical Importance: Functional L-cells are present in equine large intestine, although their importance is unknown. No variations associated with metabolic status were identified in the coding region of equine GCG.

¹VetAgro Sup; ²Professor Equine Internal Medicine, Clinical Sciences, University of Montreal, Montreal, QC, Canada

Background: Pituitary pars-intermedia dysfunction (PPID) clinical score (CS) and TRH-Stimulation test (TRH-ST) results may vary according to several factors.

Objectives: To describe the seasonal variations of a CS combined with TRH-ST in aged ponies, and their ability to discriminate between PPIDs and non-PPIDs.

Animals: Nine crossbreed mares aged 15–28 years, kept in the same area.

Methods: CS (gradation/33 points scale), and TRH-ST results including basal ACTH concentration ([ACTH]b,), 10- and 30-min post-stimulation ([ACTH]10; [ACTH]30) were assessed monthly over one year. Results were analyzed using Shapiro-Wilk, Kruskal–Wallis and Spearman tests.

Results: Three mares were PPID, two were Controls and four were Equivocals. Median CS was statistically higher in PPIDs (18.0 ± 3.6) compared to Equivocals (6.5 ± 1.5) and Controls (4 ± 0.5) (P < 0.01). CS results showed intra-individual monthly variations attributed to haircoat changes (n = 8), and/or occurrence of several simultaneous infections (n = 5), and/or laminitis (n = 3), and/or loss of body condition in winter (n = 2). May and June allowed optimal detection of hair changes and maximal CS differences between groups.

Annual [ACTH]b, and [ACTH]10,30 were statistically different between the three cohorts (P < 0.01). October and November were the most relevant months to differentiate the three groups by measuring [ACTH]b, and May for [ACTH]10—30.

Conclusions/Clinical Importance: CS and TRH-ST monthly variations were observed. Groups were best differentiated in May using the combination of CS and TRH-ST. The correlation between TRH-ST and CS results may be variable. Further studies are needed to assess the sensitivity and specificity of the CS.

¹VetAgro Sup; ²Assistant Professor, Dermatology, VetAgro Sup; ³Professor, Dermatology, VetAgro Sup

Background: Progressive hair changes associated with Pituitary pars-intermedia dysfunction (PPID) are poorly characterized.

Objectives: To compare the variations of hair characteristics in PPIDs and aged controls.

Animals: Fifty-seven client-owned horses and ponies, at least 15-years-old, included over the course of four seasons.

Methods: At admission, a PPID-clinical score (CS/33), a TRH stimulation test, a shedding score, a jugular hair root density using dermoscopy (cm2), a trichogram assessing anagen (A)/telogen (T) ratio (%) and mean sternal hair length (cm; on 10 hairs) were performed. Results were analyzed using Shapiro-Wilk and Kruskal-Wallis tests.

Results: Twenty-six equines harboring hypertrichosis were PPID, 20 presented equivocal results, and 11 were controls. Median CS was statistically higher in PPIDs (17.0 ± 5.7) compared to Equivocals (6.0 ± 1.7) and Controls (4 ± 0.7) (P < 0.01). In healthy controls, shedding scores increased physiologically in spring and fall. Jugular hair density and sternal hair length were maximal in winter, A/T ratio increased in fall and was minimal in summer. Median jugular hair density, A/T ratio, and sternal hair length were significantly different between the 3 groups (P < 0.01). Hair changes in the PPID group were characterized by sustained anagen activity, higher hair root density and hair length throughout the year, and a time-lagged shedding score. Equids in the Equivocal group showed variable intermediate hair changes.

Conclusions/clinical Importance: Abnormal shedding and progressive hypertrichosis in PPIDs are characterized by higher hair density, longer hair and sustained anagen hair follicle activity. Further studies are warranted to evaluate the influence of season and breed on haircoat characteristics.

¹Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Melbourne, VIC, Australia; ²Senior Lecturer, Veterinary Biosciences, School of Veterinary Medicine, The University of Melbourne, Melbourne, VIC, Australia; ³Boehringer Ingelheim Vetmedica GmbH; ⁴Head of the Equine Studies Group, Mars Horse Care; ⁵Academic Lead (Research), School of Biology and Environmental Science, Queensland University of Technology, Brisbane City, QLD, Australia; ⁶Professor, Basic Vet (Preclinical) Sciences, Veterinary Biosciences, School of Veterinary Medicine, The University of Melbourne, Melbourne, VIC, Australia

Background: Equine pituitary pars intermedia dysfunction (PPID) is associated with reduced dopamine secretion and many cases are insulin dysregulated (ID), which increases laminitis risk. Dopamine agonists improve insulin sensitivity in other species, but the role of dopamine in insulin regulation in equids is unclear.

Objectives: To determine whether dopamine agonist treatment affects tissue insulin sensitivity and/or the post-prandial insulin response in ID equids, with and without PPID.

Animals: Sixteen horses and ponies with ID; eight with concurrent PPID and eight without PPID, paired by age and breed.

Methods: Animals were treated (4 weeks) with pergolide mesylate (2 μg/kg PO SID) or no drug, in a randomized crossover study. A combined glucose and insulin test (CGIT) and standard meal test (SMT; 1.2 g/kg BW starch plus 0.11 g/kg BW free sugar) were performed before and after treatment. Glucose and insulin responses were compared using a paired t-tests.

Results: Pergolide had no significant effect on insulin sensitivity as measured by the CGIT (45 min glucose and 75 min insulin), nor on the glycemic responses to the SMT, in either the PPID or non-PPID groups. However, the area under the curve for insulin following the SMT was significantly reduced in the PPID group following pergolide treatment (47251 ± 5609 μIU/ml/min vs. 27655 ± 9089, mean and SEM; P = 0.036).

Conclusions and Clinical Importance: No evidence was found for pergolide modifying systemic insulin sensitivity in insulin resistant equids with or without PPID. However, pergolide may have beneficial post-prandial insulin-lowering effects in PPID cases with ID.

¹College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA; ²Ontario Veterinary College, University of Guelph, Guelph, ON, Canada

Background: Hypocalcemia has been documented in horses with gastrointestinal disease and colitis. PTH maintains calcium homeostasis during hypocalcemia by enhancing bone resorption and renal calcium reabsorption. Markers of bone remodeling include C-terminal telopeptide of type I collagen (CTX-I; resorption) and osteocalcin (OCN; formation). The skeletal response to hypocalcemia and high PTH concentrations has not been evaluated in critically ill horses.

Objectives: To measure markers of bone resorption (CTX-I) and formation (OCN) and to determine their association with serum PTH, total calcium (tCa), ionized calcium (iCa) and phosphorus concentrations, disease severity, and mortality in horses with colitis.

Methods: Prospective, multicenter. 70 horses (55 with colitis and 15 healthy) were included. Blood samples were collected on admission. Serum CTX-I, OCN, and PTH concentrations were measured by immunoassays. Data were analyzed by non-parametric methods and univariate analysis.

Results: Serum CTX-1 and PTH concentrations were higher, while serum OCN, tCa, iCa and phosphorus concentrations were lower in horses with colitis compared to healthy ones (P < 0.05). Serum tCa and iCa concentrations were lower and PTH higher in non-surviving horses with colitis (P < 0.05). Horses with PTH concentrations >139.9 pg/mL were more likely to die (OR = 2.9; P < 0.05).

Conclusions: Increased PTH and CTX-I together with reduced OCN, tCa, iCa and phosphorus concentrations in horses with colitis are consistent with increased bone turnover to restore normocalcemia. Excessive PTH response was associated with mortality, suggesting PTH resistance. Elevated PTH and reduced iCa concentrations predicted mortality with fair sensitivity and specificity in horses with colitis.

¹College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA; ²Rood and Riddle Equine Hospital, Lexington, KY, USA

Background: Hypovitaminosis D is common in critically ill patients, including foals. In addition to calcium and phosphorus homeostasis, vitamin D has antibacterial properties through antimicrobial peptides (β-defensin-1 and cathelicidin). These peptides have not been evaluated in equine patients but could play a role in disease progression.

Objectives: To measure serum vitamin D metabolites (25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D] and determine their association with β-defensin-1 and cathelicidin concentrations, disease severity and outcome in hospitalized foals.

Methods: Prospective, multicenter study. 60 foals <72 h (hospitalized = 41; healthy = 19) were included. Blood samples were collected over 72 h to measure serum 25(OH)D, 1,25(OH)2D, β-defensin-1 and cathelicidin concentrations. Data were analyzed by non-parametric methods and univariate logistic regression.

Results: On admission, serum 25(OH)D and 1,25(OH)2D concentrations were lower in hospitalized compared to healthy foals (P < 0.05). Serum β-defensin-1 and cathelicidin concentrations were lower in all time points in hospitalized than healthy foals (P < 0.05). There was a positive correlation between serum β-defensin-1 and 25(OH)D in hospitalized foals (r = 0.72; P < 0.05). Non-surviving foals had the lowest serum 25(OH)D concentrations (P < 0.05). Hospitalized foals with serum 25(OH)D<6.1 ng/mL were more likely to die (OR = 5.1; P < 0.05).

Conclusions: Decreased antimicrobial peptides in the presence of hypovitaminosis D and their association with disease severity indicates that vitamin D directly and through its regulated genes is protective against illness in newborn foals.

College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA

Background: It was recently shown in humans and mice that there is an active regulatory system between bone (osteocalcin; OCN) and the endocrine pancreas (insulin) where OCN promotes insulin secretion and insulin stimulates osteoblast function and OCN secretion. This system (bone-pancreas loop) appears to be important in energy homeostasis (role of the skeleton on glucose metabolism). There is no information on the bone-pancreas loop in veterinary or equine medicine.

Objectives: To investigate the bone-pancreas loop in hospitalized foals by measuring serum OCN, insulin and incretins (glucagon-like peptide-1 [GLP-1] and glucose-dependent insulinotropic polypeptide [GIP]) and determine their association with disease severity and non-survival.

Methods: Prospective, multicenter. 84 newborn foals ≤3 days old (70 hospitalized; 14 healthy). Serum OCN and insulin, and plasma GLP-1 and GIP concentrations were measured over 72 h. Data analysis was carried out using non-parametric methods and univariate logistic regression.

Results: Hospitalized foals had decreased OCN, insulin and GIP, but higher GLP-1 concentrations compared to healthy ones (P < 0.05). Serum OCN concentrations were positively correlated with insulin in hospitalized foals (r = 0.5; P < 0.05). Non-surviving foals had lower OCN and insulin, but elevated GlP-1 concentrations than survivors (P < 0.05). Hospitalized foals with OCN concentrations <8.5 ng/mL were more likely to die (OR = 5.4; P < 0.05).

Conclusions: Decreased blood OCN, insulin and GIP concentrations together with elevated GLP-1 concentrations could reflect a disruption of systemic inflammation on the bone/pancreas loop to maintain energy homeostasis and osteoblast function in hospitalized foals.

¹The University of Queensland, Gatton, QLD, Australia; ²PhD Candidate, School of Veterinary Science, The University of Queensland, Gatton, QLD, Australia; ³Lecturer (Animal Science), School of Agriculture and Environmental Sciences, University of Southern Queensland, Darling Heights, QLD, Australia; ⁴Associate Professor, School of Veterinary Science, The University of Queensland, Gatton, QLD, Australia

Background: Phenylbutazone is used for the management of hyperinsulinemia-associated laminitis; however, we have shown that it alters insulin and glucose dynamics of horses with insulin dysregulation (ID).

Hypothesis/Objectives: Investigate the effect of phenylbutazone on insulin sensitivity in horses.

Animals: Seventeen University-owned adult horses including nine diagnosed with ID and eight controls.

Methods: In a randomized crossover design study with a 10-day washout period between treatments, horses received intravenous phenylbutazone (4.4 mg/kg SID) or placebo. On day eight of treatment, a modified frequently sampled intravenous glucose tolerance test (mFSIGTT) was performed. Insulin and glucose concentrations were measured with an IMMULITE1000 or a handheld glucometer respectively. Minimal model analysis was performed, and changes between treatments assessed with paired t-tests, with P < 0.05 considered significant.

Results: Phenylbutazone administration did not significantly alter insulin sensitivity in ID or control horses (P = 0.3280 and P = 0.3617, respectively) nor glucose effectiveness (P = 0.1187 and P = 0.2585, respectively). There was no significant effect on the acute insulin response to glucose in either group (P = 0.6723 and P = 0.5867). There was no significant effect on the areas under the curves for insulin (P = 0.4202 and P = 0.3171) or glucose (P = 0.6044 and P = 0.1321).

Conclusions and Clinical Importance: The changes in insulin and glucose dynamics observed after phenylbutazone administration in ID horses are not mediated by an alteration in insulin sensitivity. Further investigation into the unique mechanisms associated with phenylbutazone administration in ID horses is required.

¹The University of Queensland, Gatton, QLD, Australia; ²Associate Professor, School of Veterinary Science, The University of Queensland, Gatton, QLD, Australia

Background: Phenylbutazone is prescribed for the management of hyperinsulinemia-associated laminitis; however, non-steroidal anti-inflammatory drugs are used in diabetic people to stimulate pancreatic activity and insulin secretion. We have demonstrated that phenylbutazone decreased glucose concentration in horses with insulin dysregulation (ID); however, it did not appear directly regulated by insulin secretion.

Hypothesis/Objectives: Phenylbutazone alters pancreatic activity through the entero-insular axis in horses with ID.

Animals: Nineteen University-owned horses including 10 with ID.

Methods: In a randomized crossover trial, horses received intravenous phenylbutazone (4.4 mg/kg daily) or placebo, with a 10-day washout period between treatments. On day 9 of treatment, an oral glucose test (OGT) was performed. Insulin concentrations were measured with the IMMULITE1000, glucose with a handheld glucometer and gastric inhibitory polypeptide (GIP) with a previously validated ELISA. Changes in insulin, glucose and GIP concentrations, as well as glucose-induced secretions of insulin and GIP were analyzed with linear mixed effect models and paired tests with P < 0.05 considered significant.

Results: In horses with ID, phenylbutazone administration decreased post-OGT glucose concentrations with both lower areas under the curve (P = 0.0031) and lower maximum glucose concentrations (P = 0.0062). Although, post-OGT insulin concentrations were not altered by phenylbutazone administration (P = 0.7903), a higher glucose-induced insulin secretion was detected (P = 0.0466) which was associated with an increased glucose-induced GIP secretion (P = 0.0200). No phenylbutazone-induced changes were detected in control horses.

Conclusion and Clinical Importance: In horses with ID, phenylbutazone induces a higher pancreatic activity mediated by the entero-insulin axis.

¹Amwell Data Services, LLC; ²Boehringer Ingelheim

Background: The influence of genetics on endocrine disorders is not well understood. Evaluating endocrine disorders among different horse breeds may improve identification and management of these pathologies.

Hypothesis/Objectives: The objective was to compare PPID and ID status and frequency of endocrine-associated signs within horse breeds grouped by clade.

Animals: Horses and ponies (n = 5,605), ages 10 to 45, with endocrine-associated clinical signs were tested for endocrine disorders by their veterinarian.

Methods: A retrospective analysis was performed on veterinarian-provided data from a 2016–2020 study of ponies and horses with suspected endocrine disorders. Equids were considered PPID positive if spring basal, spring post-TRH-stimulated, or fall basal ACTH levels were >35, >110, or >50 pg/mL, respectively, and considered ID positive if basal insulin levels were >20 μIU/mL. Frequencies of PPID, ID, laminitis, and recurrent infections were analyzed using chi-square or two-way ANOVA.

Results: PPID and ID rates were highest in Clades 3 and 1 at 61.49 and 72.89 percent, respectively, and lowest in Clades 2 and 4 at 24.05 and 27.93 percent, respectively. All clades had higher rates of ID than PPID except Clades 4 and 6. Recurrent infections were least correlated with endocrine disorders (P = 0.0001) and were lowest in PPID+/ID+ horses (P = 0.0234) and clades 1–3 and 5 (P < 0.0001). Laminitis was observed more frequently in ID+ horses (P = 0.0002) and less frequently in clades 4 and 6 (P = 0.0051).

Conclusions and Clinical Importance: The observed differences in endocrine disorder frequencies among clades highlight the need to better understand the involvement of genetics within endocrine disorders.

Percentage of horses within clade

Classification of endocrine disorders (e.g., PPID and/or ID) in eight genetic clades of horses (P < 0.0001) showing the variability of these pathologies among horse and pony breeds.

¹Amwell Data Services, LLC; ²Boehringer Ingelheim

Background: Sporthorse breeds are frequently trained through upper-level equestrian disciplines. Since sporthorses often serve as schoolmasters, understanding the prevalence of endocrine disorders (“ED”) in these breeds is important.

Hypothesis/Objectives: The objective was to assess PPID and ID status and frequency of endocrine-associated clinical signs (“EACS”) within different sporthorse breeds grouped by geographic origin.

Animals: Sporthorses (n = 784), ages 10 to 35, with EACS were tested for ED by their veterinarian.

Methods: A retrospective analysis was performed on veterinarian-provided data from a 2016–2020 study of sporthorses with suspected ED. Equids were considered PPID positive if spring basal, spring post-TRH-stimulated, or fall basal ACTH levels were >35, >110, or >50 pg/mL, respectively, and considered ID positive if basal insulin levels were >20 μIU/mL. Frequencies of PPID, ID, and EACS were analyzed using chi-square or two-way ANOVA.

Results: All four geographic regions evaluated had higher rates of ID than PPID. ED were highest in German sporthorse breeds at 69.72 percent (P = 0.0331). PPID and ID rates were highest in German and Spanish sporthorse breeds at 41.73 and 57.89 percent, respectively. Irish sporthorses had the lowest rates of PPID and ID at 26.92 and 42.31 percent, respectively. Rates of Laminitis, decreased athletic performance/lethargy, and delayed/decreased shedding were similar regardless of region or endocrine classification. Regional adiposity was highest in Spanish sporthorses (P < 0.0001).

Conclusions and Clinical Importance: While clinical conclusions are limited due to sample size, particularly in Irish sporthorses, these high rates of ED and EACS highlight the need for careful management of sporthorses.

¹College of Veterinary Medicine, Michigan State University, East Lansing, MI, USA; ²Professor and Chair, Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI, USA; ³Assistant Professor, Animal and Comparative Biomedical Sciences, The University of Arizona, Tucson, AZ, USA; ⁴Laboratory Manager, Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI, USA; ⁵Assistant Professor, Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI, USA

Background: Gestational diabetes mellitus (GDM) in humans can lead to significant histological and secondary functional placental changes which contribute to fetal hypoxia and growth abnormalities. It is unknown if this occurs in horses.

Hypothesis: We hypothesize that the placenta from horses with insulin dysregulation (ID; similar to GDM) will show increased weight, villous abnormalities, and vascular lesions as compared to insulin sensitive (IS) horses.

Animals: Ten adult pregnant Arabian mares.

Methods: Case control study. Placentas were collected immediately after expulsion. The weight and gross characteristics of the placenta were recorded, along with mare reproductive history. Histological samples were collected from predetermined areas of the placenta using a Swiss roll method and were routinely sectioned and stained. Samples were randomized, read blindly and lesions were scored as not present, mild, moderate, or severe (0–3). Endocrine testing was performed on all mares. Comparisons were made between ID and IS mares using Mann-Whitney U tests, Student's t-tests, and Spearman's Correlation Coefficients (significant at P < 0.05).

Results: There were six IS mares and four ID mares. Mares with ID had more histologic lesions (villous atrophy or immaturity, thickened basement membrane, and vascular changes including proliferation, fibrinoid degeneration, edema, congestion, and hemorrhage; all p values <0.05) and heavier placental weights (P = 0.04) than IS mares. There were no significant correlations between histologic scores and age, parity, or BCS.

Conclusions and Clinical Importance: Findings from this study could support an equine translational model of placental dysfunction as well as guide peri-natal mare and foal care.

Figure 1. Mean (±standard deviation) histologic placental lesion score from insulin (IS; orange) and insulin dysregulated (ID: brown) mares. All lesions were significantly higher in ID vs. IS mare placentas. *=significant at P < 0.05.

¹Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA; ²Johnson & Wales University, Providence, RI, USA

Background: Low-dose (LD) and high-dose (HD) oral sugar tests have been compared in ponies, but further investigation is required in horses.

Hypothesis: That the HD-oral sugar test (OST) would induce significantly higher blood glucose (BG) and insulin concentrations than the LD-OST.

Animals: Twenty-four adult horses (median age 16 years) of unknown insulin status.

Methods: Horses were administered a LD-OST and a HD-OST (0.15 and 0.45 mL Karo syrup per kg body weight, respectively) 7 days apart. Test order was randomly assigned. Blood was collected at T0, T60, and T90 minutes, with BG measured using a handheld glucometer and insulin measured using radioimmunoassay at a commercial veterinary laboratory. Results were compared using Wilcoxon matched-pairs signed-rank testing and bias between methods was assessed using Bland-Altman plots.

Results: Median BG and insulin at T0 were not significantly different between methods (P>0.05). Median BG and insulin were significantly higher for the HD-OST than the LD-OST at both T60 (P < 0.02) and T90 (P < 0.01). Mean bias for HD-OST glucose concentrations was 6.8% at T60 and 10.5% at T90, compared to the LD-OST. Mean bias for HD-OST insulin concentrations was 35.4% at T60 and 44.1% at T90 compared to the LD-OST. Using established cutoffs, ID was diagnosed in one horse using the LD-OST and two horses using the HD-OST.

Conclusion: HD-OST yielded significantly higher BG and insulin concentrations at both T60 and T90 than LD-OST. Test performance should now be investigated in horses with results that fall closer to cutoff values.

¹Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA; ²Johnson & Wales University, Providence, RI, USA

Background: The Wellness Ready insulin assay (WR-INS) is now available to assess insulin status in horses. An independent comparison of this assay with the radioimmunoassay for insulin (RIA-INS) is warranted.

Hypothesis: That WR-INS concentration would correlate closely with RIA-INS concentration in horses.

Animals: Twenty-four adult horses (median age 16 years) undergoing routine oral sugar testing to assess insulin status.

Methods: 144 EDTA whole blood samples were collected from horses undergoing low-dose and high-dose oral sugar tests in a companion study. WR-INS was performed immediately after sample collection; the remaining sample was centrifuged to separate plasma, which was stored at −80°C until radioimmunoassay analysis at a commercial veterinary laboratory. Results were compared using Spearman correlation, Wilcoxon matched-pairs signed-rank testing; bias between methods was assessed using Bland-Altman plots.

Results: Insulin concentration for 78 samples (54%) fell within the working range of the WR-INS assay (20.0–99.9 μIU/mL). WR-INS and RIA-INS results had good correlation for these 78 samples (rs = 0.84, P < 0.001). For these time points, median insulin concentrations were significantly higher (P < 0.001) for WR-INS concentrations compared to RIA-INS concentrations. A mean bias of 17% was detected for WR-INS compared to RIA-INS concentrations. Using previously established relevant insulin thresholds for the low- and high-dose oral sugar tests, two horses (8%) had positive results using the WR-INS and negative results with the RIA-INS.

Conclusion: WR-INS concentrations are well correlated with RIA-INS results; however, the WR-INS results are significantly higher than RIA-INS, which warrants consideration when interpreting WR-INS assay results.

North Carolina State University, Raleigh, NC, USA

Background: Colic remains the most prevalent and challenging disease in horses. Increased mortality in horses with gastrointestinal disease has been associated with insulin resistance and glucose dysregulation. Dysfunction of the enteroinsular axis (EA), characterized by abnormal concentrations of insulin-regulating incretins, may contribute to insulin dysregulation, disease progression, and poor outcome in equine colic.

Hypothesis/Objectives: We hypothesized that the concentration of incretins glucagon-like peptide-1 (GLP-1), glucagon-like peptide-2 (GLP-2), and glucose-dependent insulinotropic polypeptide (GIP) would be decreased in horses presented for colic when compared to healthy and associated with non-survival.

Animals: 10 healthy horses and 19 horses with colic (>1-year-old).

Methods: Incretin concentrations were determined in all horses on admission and at 24, 48, 72 and 96 h of hospitalization in this prospective, longitudinal study. Plasma concentration of incretins was measured with ELISA kits previously validated for horses.

Results: In healthy horses, GIP concentration increased at 48, 72 and 96 h compared to baseline (P < 0.01). At 24 h, GIP concentration was lower in horses with colic compared to healthy (P < 0.05). There were no differences in GLP-1 and GLP-2 concentration between time points and group of horses (P > 0.05). GLP-1 concentration was lower in non-survivors compared to survivors on admission (P < 0.05). There were no differences in GIP and GLP-2 between survivors and non-survivors (P > 0.05).

Conclusions and Clinical Importance: The EA dysfunction was characterized by decreased concentration of GIP in horses with colic during the first 24 h of hospitalization. GLP-1 may be used as a prognosticating factor in horses presented with gastrointestinal disease.

¹Boehringer Ingelheim Animal Health USA, Inc.; ²Middle Tennessee State University, Murfreesboro, TN, USA; ³Associate Professor, Agriculture, Middle Tennessee State University, Murfreesboro, TN, USA

Hypothesis: This study evaluated a hypothesis that the thyrotropin releasing hormone (TRH) stimulation procedure repeated at weekly intervals would yield reproducible diagnosis of Pituitary Pars Intermedia Dysfunction (PPID). Understanding TRH-stimulation repeatability is useful if TRH-stimulation testing is initiated but unable to be completed or when PPID research protocols require multiple days of testing. The protocol was approved by the Institutional Animal Care and Use Committee.

Animals: Five PPID-positive and 5 PPID-negative horses were used.

Methods: Basal blood samples were collected, then 1 mg TRH given IV, and blood collected 10 and 30 min after TRH-stimulation, then repeated on days 7, 14, and 21. Immulite assay analyses of T0-ACTH, T10-ACTH, T30-ACTH on Day 0 vs. subsequent days were compared using a mixed model with repeated measures, Pearson's correlation coefficients, and Bland-Altman plots.

Results: There was no Day effect on T0-ACTH or T30-ACTH in PPID-Negative or PPID-Positive horses, or T10-ACTH in PPID-Negative horses. In PPID-Positive horses, T10-ACTH was lower on Day 14 (P < 0.036) than Days 7 and 21. While statistically significant, these differences were not clinically relevant, as ACTH remained above the PPID-Positive diagnostic cutoff. Bland-Altman plots indicated a Day bias in PPID-Negative horses of -1.97, -0.2, and 2.5 pg/mL at T0-ACTH, T10-ACTH, and T30-ACTH respectively; Day bias in PPID-Positive horses was 44.3, 8.7, and 62 pg/mL at T0-ACTH, T10-ACTH, and T30-ACTH respectively. The Immulite inter-assay CV was 9.3%, accounting for observed Day biases.

Conclusions and Clinical Importance: TRH-stimulation test repeated at weekly intervals for 21 days provided consistent results.

¹Boehringer Ingelheim Animal Health USA, Inc.; ²Professor, Middle Tennessee State University, Murfreesboro, TN, USA; ³Associate Professor, Middle Tennessee State University, Murfreesboro, TN, USA

Hypothesis: Compared to resting (T0-ACTH), dynamic ACTH evaluation 30 min after TRH-stimulation (T30-ACTH) will provide more reliable diagnostic for PPID. T30-ACTH diagnostic cut-off values will be established.

Animals: The protocol was approved by the Institutional Animal Care and Use Committee, with 15 PPID-positive, 15 PPID-negative horses used.

Methods: In Fall and Spring, blood samples collected before and 30 min after 1 mg TRH IV were analyzed using the Immulite assay. Using T30-ACTH, the upper 95% level of PPID-Negative horses and the lower 95% level of PPID-Positive horses quantified highest Negative and lowest Positive diagnostic limits.

Results:

During Fall

Mean ± SE of T0-ACTH and T30-ACTH, respectively, was 56.8 ± 13.4 and 98.4 ± 19.9 pg/mL in PPID-Negative; 229 ± 63 and 547 ± 106 pg/mL in PPID-Positive. The T30-ACTH 95% Confidence Interval was 55.8–141 pg/mL in PPID-Negative, 320–774 pg/mL in PPID-Positive horses. Recommended Fall cutoffs are PPID-Negative <141 pg/mL and PPID-Positive >320 pg/mL.

During Spring

Mean ± SE of T0-ACTH and T30-ACTH, respectively, was 13.8 ± 2.5 and 21.5 ± 3.9 pg/mL in PPID-Negative; 129 ± 81 and 300 ± 107 in PPID-Positive. The T30-ACTH 95% Confidence Interval was 13.1–30.0 pg/mL in PPID-Negative and 70–530 pg/mL in PPID-Positive horses. Recommended Spring cutoffs are PPID-Negative <30 pg/mL and PPID-Positive >70 pg/mL.

Conclusions: PPID-Negative horses showed similar variation for T0-ACTH and T30-ACTH during Fall and Spring, but PPID-Positive horses had greater variation at T0-ACTH versus T30-ACTH during Fall and Spring, suggesting T30-ACTH is a more reliable test.

¹Texas Tech University, Lubbock, TX, USA; ²Graduate Student, Small Animal Clinical Sciences, Texas A&M University, College Station, TX, USA; ³Research Assistant Professor, Small Animal Clinical Sciences, Texas A&M University, College Station, TX, USA; ⁴Professor, Small Animal Clinical Sciences, Texas A&M University, College Station, TX, USA

Background: Horses with colitis have changes in their fecal microbiome composition based upon 16S rRNA gene sequencing. As multiple bacteria can occupy the same ecological niche, changes in taxonomic composition do not always correspond to changes in microbiome function. Shotgun sequencing is a more accurate way to predict functional microbiome changes by directly measuring functional genes. These changes caused by colitis-associated dysbiosis in horses have not been described.

Hypothesis/Objectives: We hypothesize that horses with colitis will have altered KEGG ortholog pathways compared to healthy horses and propose to quantify those changes using shotgun sequencing.

Animals: Healthy horses (n = 40) and horses with colitis caused by antimicrobial use (n = 14), Salmonella (n = 14) and Clostridia (n = 5).

Methods: DNA was extracted from feces (PowerSoil Kit, MoBio Labs, Carlsbad, CA, USA) and submitted for shallow shotgun sequencing (Boostershot, Diversigen, Minneapolis, MN, USA). A Kruskal-Wallis test followed by Tukey's HSD (Metaboanalyst 5.0) was used to identify metabolic pathways that were significantly different between groups. Significance was set at P < 0.05 for adjusted p-values.

Results: Significant differences were observed in 224/379 KEGG pathways at L2, and 404/682 KEGG pathways at L3 between groups. These pathways included bacterial transporters, secretion systems, replication factors, and toxins, among others.

Conclusions and Clinical Importance: Colitis-associated dysbiosis is correlated with a significant number of changes in KEGG pathways, indicating that there is major disruption to the functions of the microbiome. These functional changes may represent novel targets for prognostic or therapeutic purposes.

¹University of Montreal, Montreal, QC, USA; ²Private Practitioners, University of Montreal, Montreal, QC, USA; ³Assistant Professor, Pathology and Microbiology, University of Montreal, Montreal, QC, USA; ⁴Assistant Professor, Pathobiological Sciences Department, Louisiana State University, Baton Rouge, LA, USA

Background: Endoscopic digestive biopsies are commonly taken in horses with a typical clinical context of weight loss, malabsorption, hypoproteinemia and/or recurrent abdominal pain.

hypothesis/Objective: The objectives are to describe the clinical and histological findings in horses that had endoscopic duodenal and rectal biopsies taken.

Animals: This retrospective study evaluated 36 horses with digestive biopsies.

Methods: Retrospective clinical study includes horses with complete medical records that also had digestives biopsies taken at the VMTH (2017–2021).

Results: Over the past 5 years, we observed an increasing trend of endoscopic duodenal/rectal sampling at our Equine Hospital and identified 36 horses with such biopsy samples. Ten of those horses had no significant histological changes and 26 had increased immune cell infiltrations. Duodenitis/proctitis were most often described as lymphoplasmacytic (54% and 37% from duodenal and rectal tissues respectively). The infiltration intensity ranged in most cases from minimal to mild (82%) with low correlation between duodenal and rectal changes (28%) in the same patient. Horses with increased duodenal infiltrates were also more likely to have an additional diagnosis of gastric glandular ulcers (46%), compared to horses without increased duodenal infiltrates (20%).

Conclusion and Clinical Relevance: The clinical usefulness for endoscopic digestive biopsies in horses is likely more important than previously described in the literature and lymphoplasmacytic enteritis is the most frequent histological finding. The histological interpretation of both duodenal and rectal biopsies in equine patients provides a more complete evaluation of the infiltrating immune cells and their intensity.

¹University of Guelph, Guelph, ON, Canada; ²Clinica Equina Equine Hospital; ³Assistant Professor, Clinical Studies, University of Guelph, Guelph, ON, Canada; ⁴Population Medicine, University of Guelph, Guelph, ON, Canada

Background: Early and accurate identification of ischemic strangulating lesions of the small intestine (SISO) and large colon (LCSO) is crucial to reduce complications and increase survival of horses with colic. The predictive value of Peritoneal (PL) and blood (BL) lactate ratio (PL:BL ratio) and PL-BL difference for SISO and LCSO is still unclear.

Objective: Determine whether PL:BL ratio and PL-BL difference values are sensitive indicators of SISO and LCSO in horses with colic.

Animals: 58 horses with SISO, 71 non-SISO, 204 non-LCSO, and 38 LCSO.

Methods: Retrospective case-control study. Final diagnosis was retrieved from medical records. Diagnosis of SISO and LCSO was made in surgery or necropsy. Non-SISO diagnoses included: proximal enteritis (n = 23), ileal impaction (n = 41) and others (n = 7). Non-LCSO included nephrosplenic entrapment (n = 48), gas colic (n = 36), impaction (n = 38), colitis (n = 27), right dorsal colon displacement (n = 27), others (n = 28).

Results: A PL:BL ratio of 1.5 had a sensitivity and specificity of 0.67 and 0.65 and 0.71 and 0.76 for detection of SISO and LCSO, respectively. The AUC-ROC for this PL:BL ratio cut-point was 0.66 and 0.73 for SISO and LCSO, respectively. A PL-BL difference of 2.2 mmol/L and 2.6 mmol/L had a sensitivity and specificity of 0.79 and 0.82 and 0.79 and 0.88 for detection of SISO and LCSO, respectively. The AUC-ROC for PL-BL difference was 0.79 and 0.84 for SISO and LCSO, respectively.

Conclusions: PL:BL ratio and PL-BL difference can be used for diagnosis of SISO or LCSO, although PL-BL difference may be a better predictor of strangulating lesions.

¹College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA; ²North Carolina State University, Raleigh, NC, USA

Background: A common mechanism of fluid loss in equine colitis is chloride secretion via the cystic fibrosis transmembrane receptor (CFTR) protein present on epithelial cells. Human rectal biopsies are used to test CFTR function and inhibition. Inhibition of CFTR is a promising target for anti-diarrheal medications, but there are no current CFTR inhibitors for equine diarrhea.

Hypothesis: Rectal organoids will swell in response to CFTR activation and this can be modulated with CFTR inhibitors.

Animals: 5 adult healthy horses (four mares, one gelding; age range: 3–21 years) from NC State Research herds or donated for research.

Methods: Rectal biopsies were obtained under sedation or post-euthanasia (unrelated to study). Rectal crypts were isolated and plated to culture organoids. For all assays, organoids were passaged into 96-well plates and drug application was performed 2–3 days post-passaging. CFTR modulation was performed with the following activators (forskolin, DCEBIO, IBMX) and inhibitors (CFTRinh-172, GlyH-101). Organoid swelling was measured over time with calcein green fluorescence. Drug toxicity 2–3 days post-assay was identified with resazurin dye.

Results: Forskolin induces significant swelling in rectal organoids (Figure 1), consistent with CFTR activation, with no toxicity observed. DCEBIO, IBMX, and CFTRinh-172 minimally affected swelling, with no toxicity observed. GlyH-101 impaired forskolin-induced swelling at the highest dose tested but also exhibited toxicity.

Conclusions and Clinical Importance: Equine rectal organoids can serve as an in vitro model for chloride and fluid secretion in response to CFTR stimulation. Further experiments are necessary to identify safe and effective CFTR inhibitors for clinical use.

¹Royal Veterinary College Equine Hospital, Hatfield, England, UK; ²Equine Internal Medicine Specialist, Equine Internal Medicine, Donnington Grove Veterinary Group, Newbury, England, UK; ³Head of RVC Equine and Professor in Equine Internal Medicine, Emergency and Critical Care, Equine Internal Medicine, Royal Veterinary College Equine Referral Hospital, Hatfield, England, UK

Background: Gastric impactions (GI) have been identified as primary lesions (lone GI; LGI) or during investigation of other intestinal lesions (concurrent GI; CGI). Anecdotally, CGI resolve faster and carry a better prognosis than LGI.

Objectives: To determine clinical, laboratory and ultrasonographic findings, short- and long-term survival in horses with GI, hypothesizing that LGI carry a worse prognosis than CGI.

Animals: 71 horses from two referral hospitals (2007–2022).

Methods: Retrospective cohort study. GI were defined as feed extending to the margo plicatus after ≥24 h fasting. Clinical parameters, diagnostic findings, and outcome were compared between LGI and CGI. Long-term survival was determined by questionnaire.

Results: Twenty-seven horses had LGI and 44 had CGI. Large intestinal lesions were more common than small intestinal lesions (32/44 vs. 12/44). CGI resolved more slowly than LGI (2 days (0–8) vs 4 days (1–10); P = 0.003). Short- (LGI 17/27 vs. CGI 26/44; P = 0.74) and long-term survival (LGI 3.5 ± 1.9 years vs. CGI 2.3 ± 2.3 years; P = 0.42) were not significantly different. However, LGI were more likely to experience gastric rupture (LGI 8/27 vs. CGI 5/44; P = 0.05). LGI were 8.7 times more likely to require dietary changes (LGI 8/11; CGI 4/16; 95% CI 1.526–49.220; P = 0.01). GI recurrence rate was 21.7% (LGI 6/20; CGI 4/26; P = 0.23).

Conclusions and Clinical Importance: LGI and CGI present similarly with a comparable prognosis, though LGI are more likely to rupture. Long-term dietary changes are often necessary for LGI cases.

¹Massey University, Palmerston North, New Zealand; ²School of Veterinary Science, University of Queensland, St. Lucia, QLD, Australia; ³Hong Kong Jockey Club, Hong Kong; ⁴School of Veterinary Science, Massey University, Palmerston North, New Zealand

Background: Rebound gastric hyperacidity (RGH) secondary to hypergastrinemia has been suggested to contribute to the rapid recurrence of equine squamous gastric disease (ESGD) following omeprazole discontinuation.

Objectives: To evaluate changes in serum gastrin and chromogranin A (CgA) concentrations in response to medium-term omeprazole treatment and following omeprazole discontinuation.

Animals: Fourteen mature Thoroughbred racehorses in simulated race training.

Methods: Prospective cohort study. All horses received ~4 mg/kg of oral omeprazole daily for 61 days, excluding withholding periods where treatment was stopped as part of a concurrent study (57 treatment days). Serum samples were collected on day 0 prior to omeprazole treatment, on day 1 of each week of the treatment period, and for a further five weeks post-discontinuation of treatment. Serum gastrin and CgA concentrations were analyzed using radioimmunoassay and ELISA, respectively.

Results: Median serum gastrin concentrations had a 2.5-fold increase from baseline by day 7 (P < 0.0005) but did not increase further during the treatment period. Median serum gastrin concentrations returned to baseline within 2–4 days after administration of the last dose of omeprazole. No effect of treatment or discontinuation was seen in serum CgA concentrations.

Conclusions and Clinical Importance: Serum gastrin concentrations increased in response to omeprazole treatment but returned to baseline within 2–4 days of the last dose. No effect of treatment or discontinuation was seen on serum CgA concentrations, however, accuracy of the CgA results is limited. The findings do not support the use of extended tapering protocols in horses but suggest that management practices targeted at reducing ESGD risk should be optimized in the 2–4 days following discontinuation of omeprazole.

¹University of Guelph, Guelph, ON, Canada; ²PhD Student, Clinical Studies, University of Guelph, Guelph, ON, Canada; ³MSc Student, Clinical Studies, University of Guelph, Guelph, ON, Canada; ⁴The Ohio State University, Columbus, OH, USA; ⁵Professor, The Ohio State University, Columbus, OH, USA

Background: In critically ill humans with sepsis, trauma, ischemia/reperfusion, and prolonged hyperglycemia, often lead to diffuse glycocalyx alterations that are linked to endothelial dysfunction. Endothelial glycocalyx (EG) information in healthy horses or horses with colitis is lacking.

Objective: Determine the blood concentrations of EG degradation markers in healthy horses and horses with colitis.

Animals: 19 healthy horses and 70 horses with acute colitis (52 survivors and 18 non-survivors).

Methods: Prospective case control study. Serum heparan sulfate (HS), syndecan-1 (Syn-1), and Angiopoeitin-2 (Ang-2) concentrations were determined on admission and compared among groups. Horses were classified as SIRS and non-SIRS based on alterations in body temperature, heart and respiratory rate and total white blood cells.

Results: Serum Ang-2 concentrations were significantly higher in colitis (n = 23; 820 pg/ml, 476–1562) than healthy (n = 9; 502 pg/ml, 370–534) horses (P = 0.04). Serum HS concentrations were numerically, but not statistically, higher in colitis (n = 70, median: 32 ng/ml, range: 21–45) than healthy (n = 19; 23 ng/ml, 10–42) horses (P = 0.06). Serum concentrations of EG degradation markers were not significantly different in surviving and non-surviving horses with colitis or SIRS and non-SIRS horses (P > 0.05). A significant positive correlation between HS and Syn-1 was identified in horses with colitis (r = 0.37, P < 0.0001).

Conclusions: Horses with colitis had glycocalyx injury and endothelial activation biomarkers, but an association between EG degradation markers and mortality was not identified. Investigation of the impact of therapies aiming to preserve EG integrity in horses with colitis are warranted.

¹University of Guelph, Guelph, ON, Canada; ²PhD Student, Population Medicine, University of Guelph, Guelph, ON, Canada; ³Pathobiology, University of Guelph, Guelph, ON, Canada; ⁴Assistant Professor, Clinical Studies, University of Guelph, Guelph, ON, Canada; ⁵Associate Professor, Population Medicine, University of Guelph, Guelph, ON, Canada

Background: In humans, the red blood cell distribution width (RDW), monocyte-to-lymphocyte count ratio (MC:LC ratio), platelet-to-lymphocyte count ratio (PC:LC ratio), mean platelet volume (MPV), and MPV-to-PC ratio (MVP:PC ratio) are associated with mortality in septic patients. The prognostic value of these variables in critically ill horses is unknown.

Objective: Investigate whether RDW, MC:LC ratio, PC, PC:LC ratio, MPV, and MPV:PC ratio can predict the mortality of horses with acute colitis.

Animals: 131 horses >1-year-old with colitis. Composed of 102 surviving and 29 non-surviving horses.

Methods: Retrospective cohort study. Colitis was defined as a horse with diarrhea and leukopenia (total white blood cell count <5×109 cells/L) on admission. Data from admission CBC were used. Survival was defined as discharge from hospital. Data were analyzed by non-parametric methods and multivariate analysis.

Results: The WBC, RDW, MC, PC, MC:LC ratio, and MPV:PC ratio were lower in non-surviving than surviving horses with colitis (P < 0.05, for all comparisons). Colitis horses with lower RDW (OR: 2.28, 95% CI: 1.29 to 4) and PC (OR:1.02, 95% CI: 1.01 to 1.03) values were more likely to die or being euthanized.

Conclusion: RDW and PC are independent prognostic markers of mortality in horses with colitis. These variables can be used as markers of systemic dysfunction and a dysregulated inflammatory response in critically ill horses.

¹Ross University School of Veterinary Medicine, Basseterre, St. Kitts; ²Head of Department, Clinical Sciences, Ross University School of Veterinary Medicine, Basseterre, St. Kitts; ³Associate Dean for Academic Affairs/Chief Academic Officer, Ross University School of Veterinary Medicine, Basseterre, St. Kitts; ⁴Assistant Professor, Clinical Sciences, Ross University School of Veterinary Medicine, Basseterre, St. Kitts

Background: Developing manual, noncommercial platelet-rich plasma (PRP) production methods in donkeys would facilitate cost-efficient field management of various diseases in a species often treated under resource-limitations.

Objectives: To evaluate two methods of PRP production validated in horses (double [DC] versus single centrifugation [SC]) in donkeys.

Animals: Six healthy adult donkeys from a research herd.

Methods: Whole blood (WB) collected into either a citrate-phosphate-dextrose-adenine blood bag or sodium citrate vacutainer tubes subsequently underwent DC or SC, respectively, to produce PRP. Three collections were performed two weeks apart per animal. Concentrations of platelets ([PLT]), leukocytes ([WBC]), and erythrocytes ([RBC]), and platelet-derived growth factor-BB (PDGF-BB) activity were assessed in WB and PRP derived from both methods.

Results: Both protocols concentrated platelets 1.7–5.2-fold, reduced WBC 1.1–50.4-fold, and decreased RBC at least 829-fold compared to WB (P < 0.0001). Activity of PDGF-BB in DC-PRP and SC-PRP increased 1.2–7.0-fold in comparison to WB (P < 0.003). In DC-PRP, [PLT] was 3-fold (P < 0.0001) and PDGF-BB activity 5.8-fold (P = 0.0007) higher compared to SC-PRP. Reduction in [WBC] and [RBC] was 42-fold and 22-fold greater, respectively, in SC-PRP than DC-PRP (P < 0.0001), but [WBC] did not differ between WB and DC-PRP (P = 0.61). Double centrifugation yielded higher [PLT] and PDGF-BB activity in PRP despite greater WBC and RBC contamination than SC.

Conclusions and Clinical Importance: Manual, noncommercial methods of equine PRP preparation can be used to produce PRP in donkeys. Future studies are necessary to determine the in vivo efficacy of asinine PRP.

¹University of Illinois; ²Large Animal Internal Medicine Resident, Department for Veterinary Clinical Medicine, University of Illinois; ³Equine Surgery Resident, Department for Veterinary Clinical Medicine, University of Illinois; ⁴Equine Surgery and Medicine Intern, Department for Veterinary Clinical Medicine, University of Illinois; ⁵Clinical Associate Professor, Department for Veterinary Clinical Medicine, University of Illinois; ⁶Department Head and Professor, Department for Veterinary Clinical Medicine, University of Illinois; ⁷Assistant Clinical Professor, Department for Veterinary Clinical Medicine, University of Illinois; ⁸Professor of Equine Internal Medicine, Department of Clinical Veterinary Medicine, University of Illinois

Background: Coagulopathy is common in equine critical disease with early recognition crucial for patient management and prognosis. Increased red blood cell mass (RCM) creates viscoelastic (VE) hypocoagulable profiles in dogs and horses. While small animal studies show in vitro VE hypercoagulability with decreased RCM, there are no data in horses to date.

Hypothesis/Objectives: Acepromazine induced splenic volume increase is associated with decreased RCM and altered VE profiles.

Animals: Eight healthy adult horses from the University of Illinois research herd.

Methods: Non-randomized, controlled experimental study. Acepromazine (0.1 mg/kg) IV. CBC, fibrinogen, PT, PTT, PCV, TP and VE testing with VCM Vet performed stallside: pre-acepromazine administration(T0), 1 h post(T1) and 12 h post(T2). Splenic volumes determined ultrasonographically. One-way repeated measures ANOVA was performed to determine the effect of time (sample) on the VCM Vet and CBC parameters, as well as spleen volume. Where a significant effect was identified (P < 0.05), pair-wise comparisons between groups were performed by Tukeys HSD.

Results: PCV decreased ~13% following acepromazine administration, P < 0.001 (T1–T0 P < 0.001; T2–T0 P < 0.001; T2–T1 P < 0.001). MCF (maximal clot firmness) increased P = 0.04 (T0–T1 P = 0.03), WBC decreased P < 0.001(T1–T0 P < 0.001; T2–T1 P = 0.006), and splenic volume increased P = 0.045 (T1–T0 P = 0.04). No other examined variables were significantly altered.

Conclusions and Clinical Importance: This normovolemic non-inflammatory acute model of equine anemia demonstrated both VE hypercoagulability-increased MCF- and splenic volume increase. A normovolemic subacute RCM removal anemia model in dogs, using native uncitrated blood, demonstrated in vitro VE hypercoagulability as decreased CFT (clot formation time), with increased alpha and MCF, potentially artefactual. Horse blood may be similar.

¹Department of Clinical Sciences, Kansas State University, Manhattan, KS, USA; ²Clinical Assistant Professor, Equine Internal Medicine, Clinical Sciences, Kansas State University, Manhattan, KS, USA; ³Associate Dean of Clinical Programs, Department Head and Professor, Equine Internal Medicine, Kansas State University, Manhattan, KS, USA; ⁴Clinical Professor and Section Head, Equine Medicine and Surgery, Clinical Sciences, Kansas State University, Manhattan, KS, USA; ⁵Clinical Professor, Equine Field Service, Clinical Sciences, Kansas State University, Manhattan, KS, USA; ⁶Executive Director, Veterinary Medical Continuing Education, Edgar E. and M. Elizabeth Coleman Chair Food Animal Production Medicine; and Professor, Production Medicine, Clinical Sciences, Kansas State University, Manhattan, KS, USA

Background: Serum amyloid A (SAA) is an acute phase protein. Routine vaccination is intended to induce an antigen-specific inflammatory response. In some instances, this response can be debilitating. Characterizing the acute phase inflammatory response after vaccination in healthy horses will provide a baseline for expected SAA expression.

Hypothesis/Objectives: The objective was to measure the effect of routine vaccination on SAA concentrations in apparently healthy horses. It was hypothesized that SAA would increase following routine vaccination compared to placebo administration.

Animals: Apparently healthy client-owned horses (n = 21) and Kansas State University College of Veterinary Medicine teaching horses (n = 15) were included.

Methods: In Experiment 1 (n = 8), a blinded, randomized, prospective, cross-over study was performed. Horses were either vaccinated (rabies, tetanus, West Nile, Eastern and Western equine encephalomyelitis, equine herpesvirus-1/-4, influenza) or administered saline, and SAA was measured at 6, 12, and 24 h and daily until day 10. In Experiment 2 (n = 28), a prospective, observational study measured SAA post-vaccination at 12 and 24 h and daily until day 10.

Results: Over time, vaccination resulted in increased SAA concentrations compared to placebo without clinical evidence of an adverse reaction. The median SAA post-vaccination peaked on day 2 (median 1872 μg/ml, interquartile range: 0–2, 402.5) and returned to normal (<20 μg/ml) by day 9 (median 6 μg/ml, interquartile range: 0–23.5) post-vaccination.

Conclusions and Clinical Importance: Routine vaccination results in an increased SAA. This provides evidence for a period of convalescence following vaccination. Measuring SAA following vaccination cannot be used as an indicator of illness.

¹School of Veterinary Medicine, Texas Tech University, Lubbock, TX, USA; ²Research Professor, School of Veterinary Medicine, Texas Tech University, Lubbock, TX, USA

Background: Intradermal skin testing in horses is a complicated and time-consuming procedure in ambulatory settings. Few recommendations currently are available for the selection of time points to evaluate.

OBJECTIVE: Compare the results of intradermal skin testing between 15 and 30 min to identify the optimum time for observations in ambulatory settings.

Animals: 17 client-owned horses in Texas.

Methods: All horses were clipped and prepped for intradermal skin testing of 23 allergens, 1 positive control (histamine), and 1 negative control (saline). Lesions sides were measured by the maximum diameter 15 and 30 min post-injection. Saline ratio, histamine ratio, and severity were calculated for each lesion.

Results: Statistically significant differences in diameter were identified in 13/23 allergens; however, no statistical differences were found in for the saline ratio, histamine ratio, or in severity (normal, mild, severe). 5/17 horses had a minimum of 4/23 positive allergens (either severe or mild) at 15 min that were normal by 30 min. 8/17 horses had a minimum of 4/23 normal allergens at 15 min that were positive (either severe or mild) by 30 min.

Conclusions and Clinical Importance: Further work is necessary to identify the relevance of temporal changes in lesions size when evaluating intradermal skin testing results. Evaluation of multiple time points may be useful for the identifying positive allergens.

¹Ontario Veterinary College, University of Guelph, Guelph, ON, Canada; ²University of Guelph, Guelph, ON, Canada; ³Ohio State University, Columbus, OH, USA

Background: Hypovitaminosis D is associated with mortality in critically ill foals. Vitamin D concentrations [VitD] in horses with colitis has not yet been studied.

Objectives: Determine the [VitD] in healthy horses and horses with colitis and their association with mortality and the severity of the disease.

Animals: Twenty-five healthy and eighty-nine horses with colitis.

Methods: Prospective case-control study. Serum [VitD] were measured on admission in horses with colitis. Survival was determined by hospital discharge. Horses were classified as SIRS and non-SIRS based on alterations in body temperature, heart and respiratory rate, and total white blood cells. Blood concentration of creatinine was also recorded on admission. Data was analyzed by non-parametric methods.

Results: [VitD] were not statistically different between healthy (9.7 ng/ml [4.9–29.6]) and horses with colitis (10.3 ng/ml [3.5–31.3]; P = 0.96). In horses with colitis, [VitD] were not different between survivors and non-survivors (10.4 ng/ml [4.5–31.3] vs. 10.0 ng/ml [3.5–20.9]; P = 0.98). Horses with colitis that had SIRS and azotemia (creatinine >130 μmol/L) had significantly lower [VitD] (9.7 ng/ml [3.5–17.0]) than those without SIRS and azotemia (10.8 ng/ml [4.5–31.3]; P < 0.05). The survival proportion of horses with colitis, SIRS and azotemia was lower than horses with colitis without these alterations (P = 0.04).

Conclusions and Clinical Importance: There were no statistical differences in [VitD] between healthy and horses with colitis. However, horses with colitis with systemic inflammation and volume depletion tend to have lower [VitD] and are less likely to survive.

¹University of California Davis, Davis, CA, USA; ²Massachusetts General Hospital, Boston, MA, USA; ³Merck Animal Health, Madison, NJ, USA

Background: Strangles has remained a very important respiratory disease in horses worldwide, with little epidemiological studies available.

Hypothesis/Objectives: The aim of the study was to describe selected epidemiological aspects of horses with acute onset of fever and respiratory signs testing qPCR-positive for Streptococcus equi subsp. equi (S. equi).

Animals: 9409 horses with acute onset of fever and respiratory signs from all regions of USA were included in a voluntary biosurveillance program from 2008 to 2020.

Methods: Information pertaining to demographics, location, season, clinical signs, and vaccination status was collected. Nasal swabs were collected and tested via qPCR for S. equi and common respiratory viruses including equine influenza virus, equine herpesvirus-1/-4, and equine rhinitis A/B virus.

Results: A total of 715 (7.6%) of study horses tested qPCR-positive for S. equi, of which, 226 (32%) had coinfections. The median age for the S. equi qPCR-positive horses was 8 ± 4 years and nasal discharge (639%–89%) and fever (590%–83%) were the most common clinical signs reported in these horses. There was a significantly greater number of horses testing qPCR-positive for S. equi during winter and spring compared to summer and fall (P < 0.001). Also, there was a significant difference (P = 0.001) in the frequency of reported S. equi vaccination between S. equi qPCR-positive (89 horses) and S. equi qPCR-negative cases (824 horses).

Conclusions and Clinical Importance: The qPCR prevalence of S. equi in the USA was 7.6%, supporting the endemic occurrence of strangles. Further, horses vaccinated against S. equi were less likely to test qPCR-positive against S. equi.

¹University of Guelph, Guelph, ON, Canada; ²BSc Student, University of Guelph, Guelph, ON, Canada; ³Intern, University of Guelph, Guelph, ON, Canada; ⁴The Ohio State University, Columbus, OH, USA; ⁵Professor, The Ohio State University, Columbus, OH, USA

Background: The endothelial glycocalyx (EG) regulates vascular permeability, provides anti-coagulant and anti-adhesive effects on the surface of endothelial cells, and can shield endothelial cells from oxidative stress. Pathological injury to the glycocalyx occurs in ischemia-reperfusion, inflammation, sepsis, and shock.

OBJECTIVE: Determine the blood concentrations of EG degradation markers in healthy, sick-non septic (SNS) and septic foals.

Animals: 15 healthy, 13 SNS and 33 septic foals. Sick foals were further divided into 34 survivors and 11 nonsurvivors.

Methods: Prospective case control study. Plasma heparan sulfate (HS), syndecan-1 (Syn-1), and Angiopoeitin-2 (Ang-2) concentrations were determined on admission and compared among groups.

Results: Plasma HS concentration was significantly higher in septic (n = 33, median: 48 ng/ml, range: 43–55) than healthy (n = 15; 37 ng/ml, 19–49) foals (P = 0.02). Ang-2 concentration was also higher in septic (n = 19; 1110 pg/ml, 792–1388) than healthy (n = 8; 810 pg/ml, 392–520) foals (P = 0.04). No differences in plasma Syn-1 concentrations were identified among healthy, SNS and septic foals, but Syn-1 was higher in non-surviving (n = 11; 22 ng/ml, 9.5–28) than surviving (n = 34; 48 ng/ml, 43–55) foals (P = 0.026). No other differences were present between surviving and non-surviving foals. A significant correlation between HS and Syn-1 was identified (r = 0.54, P < 0.0001).

Conclusions: Foals with sepsis had glycocalyx injury and endothelial activation biomarkers. EG degradation markers are associated with the outcome of survival in sick foals. Investigation on the pathophysiological importance of EG degradation in septic foals and the impact of therapies aiming to preserve EG integrity are warranted.

¹Veterinary Medicine Teaching Hospital, University of California-Davis, Davis, CA, USA; ²Professor, Medicine and Epidemiology, University of California-Davis, Davis, CA, USA

Background: The effect of intravenous dexamethasone on the antibody response to a commercial EIV/EHV-1/EHV-4 vaccine in healthy adult horses has not been investigated.

Hypothesis: Dexamethasone will result in decreased systemic inflammatory response measured by SAA and decreased antibody titers against EIV and EHV-1 post-vaccination.

Animals: 55 healthy adult horses from the research herd of School of Veterinary Medicine, University of California, Davis.

Methods: Randomized cohort study, four study groups. Healthy control (group 1), vaccination only (EIV/EHV-1, Prestige 2, Merck Animal Health, group 2), vaccination and single dose intravenous dexamethasone (20 mg, group 3), vaccination and intravenous dexamethasone every 24 h for three doses (20 mg each dose, group 4). Serum SAA levels were measured on day 1 and at 72 h. Antibody titers against EIV (hemagglutination inhibition assay, Kentucky 2014 antigen) and EHV-1 (multiplex ELISA targeting total IgG and IgG 4/7) were measured on day 1 and day 30.

Results: Only group 2 showed a significant increase in SAA values after 72 h (P = 0.04). There was no statistical difference between pre- and post-vaccination levels of anti-EHV-1 antibodies (P > 0.05). Group 2 and 3 showed a significant increase in anti-EIV antibody titers (P = 0.05 and P = 0.01, respectively). There was no significant difference between the anti-EIV IgG titers in other study groups.

Conclusion: Dexamethasone reduced the SAA response post EIV/EHV-1/EHV-4 vaccine but resulted in similar antibody responses to EHV-1 when compared to vaccinated horses only. A single dose of dexamethasone significantly increased the antibody response to EIV.

¹University of Kentucky, Lexington, KY, USA; ²Visiting Scholar, Veterinary Science, University of Kentucky, Lexington, KY, USA; ³Associate Professor, Veterinary Science, Lexington, KY, USA; Veterinary Diagnostic Laboratory, University of Kentucky, Lexington, KY, USA; ⁴Assistant Professor, Veterinary Science; Veterinary Diagnostic Laboratory, University of Kentucky, Lexington, KY, USA; ⁵Professor, Veterinary Science, University of Kentucky, Lexington, KY, USA

Background: Reactivation of latent EHV-1 can result in horizontal spread, leading to abortion and/or myeloencephalopathy (EHM). Historically, the trigeminal ganglion (TG) and upper respiratory tract associated lymphatics (RALT) have been identified as latency sites. An experimental EHV-1 infection study suggested additional sites of EHV-1 persistence after recent intranasal infection.

Hypothesis/Objectives: Alternative sites of EHV-1 persistence exist and can be detected in a random horse population.

Animals: Animals included 26 horses or ponies over 1 year of age with a postmortem interval less than 24 h, submitted to the University of Kentucky Veterinary Diagnostic Laboratory (UKVDL) for necropsy.

Methods: The trigeminal ganglion (TG); dorsal root ganglion (DRG); sympathetic trunk (ST); pharyngeal roof (PhR); retropharyngeal (retLn) and mesenteric (mesLn) lymph nodes. Tissues were formalin fixed and paraffin embedded. Block sections underwent DNA extraction (QIAamp FFPE tissue kit, QIAGEN, Germany). Semi-quantitative polymerase chain reaction (sqPCR) was used to estimate EHV-1 genomic DNA.

Results: 17 male and 9 female (predominately Thoroughbred) horses with age range 1–25 years (8.90 ± 6.89; median = 7; mode 2) were included. Results are reported in table 1.

Conclusion and Clinical Importance: This study confirms the TG and RALT as tissues of EHV-1 persistence. However, EHV-1 genome copies were more frequent in PhR than in retLn. This is the first reported detection of EHV-1 genome in the ST of a random horse population. High abundance of EHV-1 genome in 2 PhR suggests lytic infection. A larger sample size is required for independent confirmation.

¹Cornell University, Ithica, NY, USA; ²College of Veterinary Medicine, Cornell University, Ithica, NY; ³Serology/Immunology, College of Veterinary Medicine, Cornell University, Ithica, NY, USA; ⁴Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA; ⁵School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA

Background: Borrelia burgdorferi was identified in one case of equine cranial nuchal bursitis (CNB) with elevated serum OspA antibody value, warranting further investigation.

Objectives: To determine the significance of elevated serum OspA antibodies in cases of equine CNB and its correlation with the molecular identification of B. burgdorferi in bursal tissue or synovial fluid. Additionally, to compare the histologic changes in CNB with and without detection of B. burgdorferi.

Animals: Eighteen horses from the northeastern United States with PCR-confirmed Borrelia burgdorferi-associated CNB and 15 controls with normal cranial nuchal bursa, all unvaccinated for B. burgdorferi. Eleven additional horses with histologic diagnosis of CNB and B. burgdorferi PCR were included.

Methods: Retrospective multicenter cohort study (2013–2022). Medical records from horses with a diagnosis of CNB and B. burgdorferi PCR testing on CNB tissue or synovial fluid were reviewed. Serum equine Lyme multiplex assay results were compared between these and controls using an unpaired t-test. Histologic findings in cranial nuchal bursa tissue were compared between CNB cases with and without B. burgdorferi PCR detection.

Results: Serum OspA antibody values in B. burgdorferi positive cases were significantly elevated (P < .001) in horses with CNB (n = 12) compared to controls (n = 15; Figure 1). Histopathology did not vary between CNB cases with and without B. burgdorferi PCR detection.

Conclusions: Increased serum OspA antibodies are associated with the presence of B. burgdorferi in the cranial nuchal bursa of horses. The role of this pathogen in equine CNB may be underestimated and targeted therapy requires investigation.

Figure 1. OspA antibody value distribution for clinical cases of cranial nuchal bursitis (n = 12) and control horses (n = 15) compared by an unpaired t-test (P < 0.001, t(25) = 5.048)

¹University of Pretoria, Pretoria, South Africa; ²Assistant Professor in Clinical Pathology, Department of Companion Animal Clinical Studies, University of Pretoria, Pretoria, South Africa; ³Deltamune Ltd, Roodeplaat, South Africa; ⁴Professor in Veterinary Epidemiology, Department of Production Animal Studies, University of Pretoria, Pretoria, South Africa; ⁵Professor in Clinical Pathology, Department of Companion Animal Clinical Studies, University of Pretoria, Pretoria, South Africa

Background: African Horse Sickness (AHS) is caused by the African Horse Sickness Virus (AHSV). Infection results in high morbidity and mortality in naïve horses. The nature and role of the immune system and inflammatory cascade has only been investigated in vitro, in limited studies.

Hypothesis: Experimental AHSV infection results in an inflammatory response.

Animals: Four AHSV-negative horses.

Methods: Prospective, longitudinal, experimental study. Following infection with AHSV, blood was obtained q 12 h until humane euthanasia. Complete white blood cell count (WBC), serum amyloid A (SAA), iron concentration, and cytokines IL-1α, IL-2, IL-6, IL-8, IL-10, IL-12, IL-17, IFN-γ, TNF-α, and MCP-1 were measured.

Results: All horses developed severe clinical signs typical of AHS, necessitating humane euthanasia. Statistically significant changes were observed in WBC (P = 0.026); however, these were not deemed clinically relevant. Changes in acute phase reactants SAA (P < 0.001) and iron (P = 0.001) were significant but unexpectedly mild and delayed. Substantial changes in cytokine concentration were observed in TNF-α (up to 30-fold) and IL-10 (up to 150-fold) towards the final disease stages. All other cytokines remained under the detection limit or only displayed minor increases inconsistent over time and between horses.

Conclusions and Clinical Importance: Despite severe clinical signs, no horses mounted an effective inflammatory response indicated by the lack of an inflammatory leukogram and the subtle changes in acute phase reactants. The lack of a proinflammatory cytokine response is unexpected. These findings suggest viral interference with the host innate immune system resulting in a muted inflammatory response.

¹Sao Paulo State University (UNESP), São Paulo, Brazil; ²University of Guelph, Guelph, ON, Canada

Background: Diarrhea is an important clinical problem in foals. The etiological diagnosis should consider coinfections and is essential for treatment and prevention.

Hypothesis/Objectives: To detect the genetic material of the most frequently described enteric pathogens in foals with or without diarrhea.

Animals: Foals up to one year of age with diarrhea (n = 100) and controls (similar age and farms) without diarrhea (n = 100).

Methods: 3DNA and RNA extraction from fecal samples and real-time PCR (qPCR) were used to detect Salmonella spp., Clostridioides difficile and toxins A and B, Clostridium perfringens, Rhodococcus equi vapA, Cryptosporidium parvum, Giardia duodenalis, Lawsonia intracellularis, Neorickettsia risticii, Rotavirus and Coronavirus. A chi-square test was used to compare pathogen frequencies and coinfection between groups.

Results: The pathogen genetic material was detected in foals with and without diarrhea (respectively): Salmonella spp. (31%/9%; p.0001), C. difficile (39%/20%; p.003), C. difficile tox A and B (20%/8%), C. perfringens (26%/16%), R. equi vapA (33%/38%), C. parvum (17%/1%; p.0001), Giardia duodenalis (11%/10%), and rotavirus (1%/0%). L. intracellularis, N. risticii and coronavirus were not detected. Coinfections were observed in 50 of the foals with diarrhea and 26% of the control foals (p.0005).

Conclusions and Clinical Importance: There was a greater number of pathogen detections in foals with diarrhea, and a higher frequency of coinfections than controls. Salmonella, C. difficile, and C. parvum were the pathogens observed at significantly higher frequencies in these two groups. This information can be used to better understand the etiological diagnosis of diarrhea in foals.

¹Ontario College of Veterinary Medicine; ²PhD Student, Population Medicine, University of Guelph, Guelph, ON, Canada; ³Assistant Professor, Pathobiology, University of Guelph, Guelph, ON, Canada; ⁴Clinical Studies, University of Guelph, Guelph, ON, Canada; ⁵Associated Professor, Population Medicine, University of Guelph, Guelph, ON, Canada; ⁶Assistant Professor, Clinical Studies, University of Guelph, Guelph, ON, Canada

Background: Red blood cell distribution width (RDW) is a commonly reported variable on the complete blood count (CBC). It is associated with an adverse prognosis in critically ill humans. Furthermore, the neutrophil count (NC), monocyte-to-lymphocyte count ratio (MC:LC ratio), platelet-to-lymphocyte count ratio (PC:LC ratio), mean platelet volume (MPV), and MPV-to-PC ratio (MVP:PC ratio) are associated with increased mortality in septic human patients. The prognostic value of these variables in critically ill foals is unknown.

Objective: Investigate the prognostic value of RDW and other hematological variables in hospitalized ill foals.

Animals: 228 foals <3-days-old. 188 surviving and 40 non-surviving foals.

Methods: Retrospective cohort study. Variables from blood samples collected at the time of admission to the hospital were used in the analysis. Survival was defined as discharge from hospital. Data were analyzed using non-parametric methods and multivariate analysis.

Results: RDW values were similar between non-surviving and surviving foals (P>0.05). The MC and MC:LC ratio and NC were lower in non-surviving than surviving foals (P < 0.05, for both comparisons). Multivariate analysis showed that foals with lower NC (OR: 1.18, 95% CI: 1.04 to 1.35) and MC:LC ratio (OR: 7.54, 95% CI: 1.25 to 47) values were more likely to die or be euthanized.

Conclusion: RDW was not a prognostic marker of mortality in this population of hospitalized foals. However, additional studies evaluating the association of RDW with severity of disease in foals (e.g., sepsis, SIRS) are warranted. Lower neutrophil count and MC:LC ratio were associated with mortality in this population.

¹The Ohio State University, Columbus, OH, USA; ²Assistant Professor, Clinical, Equine Field Services, The Ohio State University, Columbus, OH, USA; ³Associate Professor, Clinical, Equine Internal Medicine, The Ohio State University, Columbus, OH, USA

Background: Equine anaplasmosis is a zoonotic, tick-borne disease caused by Anaplasma phagocytophilum (AP). In the United States, AP is common in the northeast and upper Midwest, although the prevalence in central Ohio is unknown.

Hypothesis/Objectives: To determine the seroprevalence of AP in healthy and febrile horses in central Ohio.

Animals: Thirty-three febrile and 259 healthy horses were included in this study. Febrile horses with concurrent respiratory disease were excluded.

Methods: A prospective surveillance study evaluated the seroprevalence of AP in apparently healthy and febrile horses in Ohio. Seropositivity was determined using the IDEXX SNAP 4Dx (SNAP) and confirmed with immunofluorescent antibody (IFA). A polymerase chain reaction (PCR) was used to detect AP in all seropositive and febrile horses.

Results: Thirty-one of 259 healthy horses were antibody-positive for AP on SNAP (31/259, 11.9%), and five of these were PCR-positive for AP (5/31, 16.1%). Nine of 33 febrile horses were PCR-positive for AP (9/33, 27%). Of the 33 febrile horses, 6 were SNAP-positive (6/33, 18%), and 1 of these was PCR-positive (1/6, 16%). IFA detected antibodies in 76% and 78% of SNAP-positive healthy and febrile horses, respectively.

Conclusions and Clinical Importance: The seroprevalence of AP in healthy horses was 11.9%, suggesting that anaplasmosis has a low seroprevalence in central Ohio. Among febrile horses, 27% were PCR-positive for AP. However, there was poor agreement between the SNAP and PCR for AP, limiting its utility in diagnosing clinical disease. Additionally, clinicians should cautiously interpret the SNAP in healthy horses, as false positives are common.

¹University of Guelph, Guelph, ON, Canada; ²Large Animal Internal Medicine, University of Guelph, Guelph, ON, Canada; ³Biomedical Science Student, University of Guelph, Guelph, ON, Canada; ⁴The Ohio State University, Columbus, OH, USA; ⁵Population Medicine, University of Guelph, Guelph, ON, Canada

Background: Alterations in total (tCa) and ionized (iCa) calcium, total magnesium (tMg), and phosphorus (Pho) homeostasis are well documented in critically ill humans and horses, and have been associated with disease severity. One study reported low iCa and high Pho concentrations in septic foals. There is limited information on calcium, magnesium, and their regulation in septic foals.

Objective: Describe blood concentrations of tCa, iCa, tMg, and Pho in septic and sick nonseptic foals, and determine their association with survival.

Animals: 144 foals <3 days of age. 91 sick non-septic (SNS) and 53 septic foals.

Methods: A retrospective case-control study. Sepsis was defined as a foal with a sepsis score >11, blood culture positive, or evidence of sepsis in the postmortem examination. Survival was defined as discharge from the hospital. Data were retrieved from medical records and analyzed by non-parametric methods and multivariate analysis.

Results: Blood concentrations of iCa and tMg were lower in septic foals compared with SNS, whereas tCa and Pho concentrations were higher in septic compared to SNS foals (P < 0.05). Positive correlations between tCa and creatinine (r = 0.26; P < 0.001), tMg and creatinine (r = 0.22; P < 0.001) were identified. Negative correlations between pH and Pho (r = −0.34 P < 0.003), pH and tCa (r = −0.27; P < 0.001), and Pho and tMg (r = −0.19; P 0.04) were also detected.

Conclusions: Alterations in iCa, tMg, and Pho in septic foals were likely consequences of endocrine dysregulation. The pH and Pho negative correlation suggests that acidemia can promote transcellular Pho redistribution in critically ill foals.

¹University of Montreal, Montreal, QC, Canada; ²Professor, Clinical Sciences Department, University of Montreal, Montreal, QC, Canada; ³Clinician, Centre Hospitalier Universitaire Vétérinaire, University of Montreal, Montreal, QC, Canada

Background: Nephrolithiasis in horses is poorly documented.

Objectives: The objectives are to describe the clinical findings, alterations in renal function and short-term survival rate of horses with nephrolithiasis.

Animals: 25 horses with nephrolithiasis presented to the Centre Hospitalier Universitaire Vétérinaire (CHUV).

Methods: Medical files from 2007 to 2021 with “nephrolithiasis” as a primary or secondary diagnosis based on ultrasonography were reviewed. Creatinine concentration was determined for 24 out of 25 cases.

Results: 25 horses (14 females, 11 males) with a wide age range (4–30 years) were included. The most common breeds were QH (5 cases) and Standardbred (4 cases). The short-term survival rate was 88% (22/25 cases) and one horse was euthanized 8 months after hospitalization for poor quality of life. Three of these four euthanized horses had grade 3 Acute Kidney Injury (AKI). Hypercreatinemia (highest value during hospitalization) were observed in 16/24 cases (67%) and grades 2 or 3 AKI were detected in 7/24 cases (29%). Nephrolithiasis was diagnosed bilaterally (56% cases) or unilaterally (44% cases), affecting the left and right kidney almost equally. Grade 2 to 3 AKI was observed in horses with unilateral (10%) and bilateral (43%) nephrolithiasis.

Conclusion and Clinical Importance: Nephrolithiasis can affect a variety of breeds, a wide range of ages, and both sexes of horses. It can be uni- or bilateral, with or without altered renal parameters, or ultrasonographic changes in the renal parenchyma. In some horses, nephrolithiasis may even be an incidental clinical findings.

¹University of Pennsylvania New Bolton Center, Kennett Square, PA, USA; ²Equine Diagnostic Solutions, Lexington, KY, USA; ³Department of Clinical Studies, University of Pennsylvania, Philadelphia, PA, USA

Background: Equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona remains an ante-mortem diagnostic challenge for some horses. Recent work suggested the use of real-time PCR (rtPCR) on cerebrospinal fluid (CSF) as a promising diagnostic tool.

Objective: To evaluate the sensitivity and specificity of S. neurona rtPCR on CSF for EPM diagnosis from horses with EPM and S. neurona-seropositive horses with other neurologic conditions.

Animals: 99 horses with neurologic disease that underwent complete neurologic examination, cerebrospinal fluid collection, and, if euthanized, neurologic necropsy.

Methods: Retrospective case-control study using biobanked CSF samples. CSF samples from neurologic horses with post-mortem confirmed EPM diagnosis, presumptive EPM diagnosis using strict criteria (SnSAG 2, 4/3 ELISA serum:CSF titer ratios <50) and horses diagnosed with other neurologic diseases were used.

Results: There were 52 horses with EPM; 23 were confirmed on postmortem exam, and 29 were presumptive clinical diagnoses. The other 47 horses all had postmortem confirmed diagnoses of other neurologic diseases including equine degenerative myeloencephalopathy (EDM), cervical vertebral stenotic myelopathy, trauma, and others. CSF samples from all horses were tested for S. neurona via rtPCR. One CSF sample was weakly positive for S. neurona by rtPCR, this sample was obtained from a horse with confirmed EDM. CSF samples from the other 98 horses were negative for S. neurona by rtPCR.

Conclusions and Clinical Importance: The results from this study contradict previous conclusions that S. neurona rtPCR is potentially useful for EPM diagnosis, as they indicate that it has a low sensitivity (0%) for EPM.

University of Pennsylvania New Bolton Center, Kennett Square, PA, USA

Background: Equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy (eNAD/EDM) is increasingly recognized as a cause of neurologic disease in adult horses. Diagnosis requires postmortem examination, with no accurate antemortem diagnostic test available. 8-hydroxy-2’-deoxyguanosine(8-OHdG), a biomarker of oxidative damage utilized in human neurodegenerative disease, has potential to correlate with postmortem diagnosis of eNAD/EDM.

Hypothesis/Objectives: We hypothesized that 8-OHdG will be increased in CSF and serum from eNAD/EDM horses compared to horses with other neurologic diseases (CVSM, EPM) and a control group of neurologically normal horses. 8-OHdG will be increased in CSF compared to serum of eNAD/EDM horses.

Animals: Case-control study using biobanked samples from 50 horses with postmortem diagnoses (20 with eNAD/EDM, 10 in each group- EPM, CVSM, and control).

Methods: A commercial competitive ELISA kit (Highly Sensitive 8-OHdG Check ELISA) previously used in a study of horses with asthma was utilized. Concentration of 8-OHdG was quantitated in both CSF and serum and compared between groups.

Results: The mean concentration of 8-OHdG amongst all groups was 179.3 pg/mL (41.5–635.4) in CSF and 150.1 pg/mL (36.8–857.5) in serum. Poisson regression showed no significant difference once confounding variables (breed, age, sample age, vitamin E concentration) were considered.

Conclusions: 8-OHdG is detectable in equine CSF and serum, although does not aid in ante-mortem diagnosis of eNAD/EDM. The findings support the concept that at the time of diagnosis horses with eNAD/EDM do not have ongoing oxidative stress, and that further studies are needed to improve our ability to obtain an antemortem diagnosis.

Figure 1. Concentration of 8-OHdG ([8-OHdG]) of both CSF and Serum compared across disease state groups. Top and bottom of box indicate first and third quartiles. Vertical lines on both the top and bottom of the box indicating minimum and maximum concentrations measured.

¹School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA; ²Tryon Equine Hospital, Columbus, NC, USA; ³Peterson Smith Equine Hospital, Ocala, FL, USA; ⁴Associate Professor, School of Veterinary Medicine, University of California Davis, Davis, CA, USA; ⁵Associate Professor of Large Animal Medicine and Neurology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA; ⁶Associate Professor of Equine Medicine, Section Chief, Internal Medicine, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA

Background: Phosphorylated neurofilament-heavy (pNF-H), a biomarker of axonal injury and degeneration, has been proposed to assist in the diagnosis of equine neurologic disease. Previous publications suggest limited utility for neonatal hypoxic-ischemic encephalopathy and equine acute grass sickness, but increased concentrations of neurofilaments seem to occur in equine protozoal myeloencephalitis (EPM), equine motor neuron disease (EMND) and cervical vertebral stenotic myelopathy (CVSM). Recently, a pNF-H ELISA became commercially available and widely utilized, particularly for horses with suspected neurodegenerative diseases including equine neuroaxonal dystrophy/degenerative myeloencephalopathy (eNAD/EDM). However, the aid of this biomarker in the diagnosis of equine neurological diseases is uncertain.

Hypothesis/Objectives: To evaluate the clinical utility of pNF-H results in horses with neurologic disease.

Animals: 178 neurologic cases recruited from three hospitals.

Methods: This retrospective study includes horses that underwent a complete neurological evaluation. Serum and cerebrospinal fluid samples were submitted for pNF-H ELISA analysis. Postmortem diagnosis was included when available.

Results: Most neurologic horses did not have increased [pNF-H]; 15 (8%) had increased serum concentrations (>1 ng/mL) and 38 (21%) had increased cerebrospinal fluid (CSF) concentrations (>3 ng/mL; Table 1). Postmortem confirmation of diagnosis was available for 65 horses and the most common diagnosis was eNAD/EDM.

Conclusions and Clinical Importance: The pNF-H testing is perceived to have a low sensitivity for any specific neurologic disease but cases with increased serum pNF-H concentration have a likely diagnosis of eNAD/EDM. Further investigations need to be done on its utility for prognosis, monitoring of progression and response to treatment in equine neurologic diseases.

¹New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA; ²Assistant Professor of Veterinary Pharmacology, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA; ³Manager, Laminitis Laboratory, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA; ⁴Associate Professor of Biostatistics, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA; ⁵Marilyn M. Simpson Associate Professor of Equine Medicine, Large Animal Internal Medicine, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA

Background: Three commonly diagnosed equine neurologic conditions in North American horses are cervical vertebral stenotic myelopathy (CVSM), equine protozoal myeloencephalitis (EPM) and equine degenerative myeloencephalopathy (EDM)/equine neuroaxonal dystrophy (eNAD), which are often clinically indistinguishable. EDM/eNAD is a diagnosis of exclusion with no confirmatory antemortem biomarkers. Cell-free DNA (cfDNA) has been associated with neurodegeneration in other species, though no studies have examined its utility in equine cerebrospinal fluid (CSF).

Hypothesis/Objectives: The objectives were to determine if equine CSF cfDNA concentrations are detectable and differ significantly between healthy control horses and those with common neurologic diagnoses, and if cfDNA is a candidate biomarker for EDM/eNAD. We hypothesized that cfDNA concentrations would be quantifiable and significantly higher in horses with EDM/eNAD compared with healthy controls and other disease states.

Animals: 45 client-owned horses with confirmed diagnoses.

Methods: Case-controlled study design. Fluorometry was used to determine biobanked CSF cfDNA concentrations from four groups (neurologically normal, CVSM, EPM and EDM/eNAD) which were compared using ANOVA and Kruskal-Wallis statistics.

Results: There were no significant differences in CSF [cfDNA] (median, IQR) between horses with EDM/eNAD (25.65 ng/mL, 18.28–30.38), CVSM (23.95 ng/mL, 17.84–37.81) or EPM (34.90 ng/mL, 29.84–37.61) and neurologically normal controls (34.95 ng/mL, 15.85–45.9), nor between disease groups (P > 0.05)(Figure 1).

Conclusions and Clinical Importance: This study is the first to evaluate cfDNA in equine CSF. Although cfDNA is a burgeoning research area, these data do not support its candidacy as a biomarker for equine neurodegenerative disease where further efforts are needed.

¹New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA; ²Valberg Neuromuscular Diagnostic Laboratory; ³Assistant Professor of Clinical Pathobiology, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA; ⁴Resident, Large Animal Internal Medicine, Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA; ⁵Marilyn M. Simpson Associate Professor of Equine Medicine, Section Chief, Internal Medicine & Ophthalmology, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA

Background: Equine degenerative myeloencephalopathy/equine neuroaxonal dystrophy (EDM/eNAD) is a common postmortem neurologic diagnosis in North American horses. Though temporal deficiency of antioxidant vitamin E is implicated in the etiology, EDM/eNAD remains a diagnosis of exclusion. A vitamin E-responsive myopathy (VEM) is diagnosed by mitochondrial alterations in highly oxidative type 1 muscle fibers in the sacrocaudalis dorsalis medialis (SCDM) muscle.

Hypothesis/Objectives: We hypothesize that mitochondrial alterations in the SCDM may be a proxy for oxidative damage to the central nervous system (CNS). The objective was to determine what percentage of horses with EDM/eNAD exhibit typical VEM histopathology. We also compared percentages of horses with EDM/eNAD exhibiting low serum vitamin E concentrations and increased serum and CSF phosphorylated neurofilament-heavy (pNF-H) concentrations.

Animals: 38 client-owned horses evaluated between 2021–2022.

Methods: Cohort study. Incisional formalin-fixed SCDM biopsies were obtained from horses with postmortem-confirmed EDM/eNAD and histopathology evaluated for mitochondrial alterations using succinate dehydrogenase A stains. Serum [vitamin E] was determined with high-performance liquid chromatography and [pNF-H] determined using sandwich ELISA.

Results: 15/38 horses (39%) with EDM/eNAD at postmortem exhibited comorbid VEM histopathology in SCDM biopsies. 3/21 (14%) exhibited increased serum [pNF-H], and 13/21 (62%) exhibited increased CSF [pNF-H]. 6/31 (19%) had low serum [vitamin E].

Conclusions and Clinical Importance: SCDM mitochondrial alterations were identified in >1/3 of horses with EDM/eNAD and can be used to increase suspicion of EDM/eNAD antemortem. Future investigation into the frequency of VEM in horses with other neurologic conditions could enable estimation of specificity.

¹University of Arizona, Tucson, AZ, USA; ²John Ewing Company, La Salle, CO, USA; ³Smalley Equine Veterinary Consulting, LLC., Omaha, NE, USA; ⁴NuSirt Bioparma Nashville, TN, USA

Background: Insulin dysregulation is the key component of equine metabolic syndrome (EMS) with management regimens focus on improving insulin sensitivity. In dogs and humans, the combination of leucine and pyridoxine has been shown to aid in weight reduction and improve insulin sensitivity. However, the effect of these supplements have not been evaluated in horses.

Objective: Determine if the combination of leucine and pyridoxine would improve EMS biochemical parameters.

Animals: A total of 38 ponies across five farms were enrolled in a 60 day trial.

Methods: Ponies were blocked by farm, age, and sex matched, and randomly assigned to the supplement (n = 20) or placebo (n = 18) group. Ponies were excluded if they were on medications or supplements labeled for the management of EMS. Ponies were evaluated using a two day testing protocol starting on day −1, 7, 30, and 60. On day one, ponies were weighed on a scale, baseline measurements (insulin, triglycerides, non-esterified fatty acids, adiponectin, and leptin) were drawn, and a two-step insulin tolerance test was performed. On day 2, an oral sugar test was performed using 0.45 ml/kg Karo light corn syrup. Chi square analyses and pairwise comparison of the estimated marginal means were performed.

Results: Ponies in the supplement group lost more weight (≥2% body weight; P < 0.04) and had a larger reduction in their max insulin concentration post oral sugar test (≥40% decrease; P < 0.03) compared to the placebo group.

Conclusion: These data suggest that this combination supplement may be used to aid in the management of EMS.

College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA

Background: Complications of intravenous catheters (IVC) are common in hospitalized horses, but specific risk factors associated with placement have not previously been investigated. Specifically, the impact of veterinary student involvement on the likelihood of complications has not been evaluated in horses.

Objectives: To investigate factors of IVC placement, including the role of individuals involved that may lead to complications such as thrombophlebitis and subcutaneous inflammation and infection.

Animals: 255 IVC placed in hospitalized adult horses over a 9-month period at a teaching hospital.

Methods: Data were collected from the electronic medical record for all horses in which an IVC was placed including the role of the individual that prepared the site and placed the IVC, site of placement, use of sedation, disease category of patient, type of catheter, reason for removal, and presence of complications at time of removal. Data were evaluated retrospectively. Univariate analyses were performed using Fisher's exact test. Significance was set at P ≤ 0.05.

Results/Findings: 41/255 (16.1%) of IVC were associated with a complication at the time of IVC removal. The relative risk of complications associated with IVCs placed by veterinary students was not significantly different to the relative risk when compared to IVCs placed by non-student personnel (P = 0.35).

Conclusions and Clinical Importance: Client perception of student involvement in procedures may affect referral decisions to veterinary teaching hospitals. The data here shows that student involvement in IVC placement does not increase the risk of complications and can be utilized to encourage client support of student involvement.

¹University of California, Davis, Davis, CA, USA; ²Hagyard Equine Medical Institute, Lexington, KY, USA; ³College of Veterinary Medicine, Cornell University, Ithaca, NY, USA

Background: Sepsis is a leading cause of mortality in neonatal foals. Early diagnosis is key to improved outcomes, but the diagnosis remains difficult. Soluble CD14 (sCD14) is a promising biomarker for inflammatory diseases in humans, including sepsis.

Hypothesis/Objectives: Sick foals have higher serum sCD14 concentrations than healthy foals, and septic foals have higher sCD14 concentrations as compared to sick, nonseptic and healthy foals.

Animals: 63 sick (29 septic, 34 nonseptic) and 26 healthy neonatal Thoroughbred foals.

Methods: Prospective observational study. Blood samples were collected from hospitalized foals at admission, d3 and prior to discharge or death, and healthy foals on days 1, 3, and 5 of life. Sick foals were categorized as septic or sick, non-septic based on sepsis score and blood culture results. Serum sCD14 was measured using a previously validated fluorescent bead-based assay.

Results: On day 3, the sick foals combined (962.0, 432.0–2002.0 ng/mL) had higher sCD14 as compared to healthy foals (769.5, 482–1154 ng/mL, P = 0.0009). At the last collection time, sCD14 was significantly greater in non-survivors (1504 ng/mL, 1443–1589) compared to surviving foals (760.0 ng/mL, 357.0–1950; P = 0.02) and healthy foals (756.0 ng/mL, 481.0–1381.0) (P = 0.03). There were no differences between septic and sick, nonseptic foals at any time point.

Conclusions and Clinical Importance: Serum sCD14 concentrations were increased in critically ill foals and non-survivors. sCD14 could be an adjunctive biomarker of neonatal health status, along with other clinical and clinicopathologic data. However, sCD14 is not necessarily specific to sepsis and there is considerable overlap between sick and healthy foals.

¹Equine Pharmacology Lab, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA, USA; ²Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA, USA

Background: Elevated plasma levels of gamma-glutamyl transferase (GGT) are frequently seen in Thoroughbred racehorses and are thought to be associated with increased training workload and poor performance.

Hypothesis: Recent training workload and current racing status influence plasma GGT levels in Thoroughbred racehorses.

Animals: 181 venous blood samples were obtained from 60 Thoroughbred racehorses in training (28 females, 16 intact males and 16 geldings, aged 1–7 years, mean: 3.1 ± 1.2 years).

Methods: Samples were obtained 1–4 h after morning workouts on a non-race day. Age, sex, whether the horse was racing (R) and number of days since last raced (DLR) was recorded. Maximum training workload on the morning of sampling (WLAM) and during the previous week (WLWK) was obtained for 131 and 90 samples respectively. Workload was categorized: none/walk/jog/gallop/breeze/race. Plasma was analyzed for GGT concentration using a Vitros XT 3400 chemistry system (Ortho Clinical Diagnostics, NJ, USA). Stepwise regression was used to identify which parameters significantly influenced GGT, then a multivariable mixed-effects regression model was used to analyze fixed effects at the level of horse nested within trainer.

Results: Median plasma GGT was 47 U/L (range: 17–142). GGT was above laboratory reference range (45 U/L) in 100/180 samples and in at least one sample from 35/60 horses. Plasma GGT levels were significantly affected by DLR and WLWK (Table 1) but not age, sex, R or WLAM (Figure 1).

Conclusion: Preliminary findings indicate further investigation of the effect of workload and performance metrics on plasma GGT levels in Thoroughbred racehorses is warranted.

Table 1. Plasma GGT model adjusted marginal means and 95% confidence intervals for days since last race (DLR) and maximum workload during previous week (WLWK)

Parameter	Nr. of horses	Marginal mean plasma GGT (U/L)	95% confidence interval
DLR
1–50	64	51.2(r)	48.06–54.32
51–100	14	54.0	50.92–57.14
101–150	10	66.8*†	60.87–72.70
151–200	12	66.6*	62.98–70.31
201–250	9	60.0*	55.48–64.48
>250	9	54.7*	51.87–57.55
WLWK
None	2	34.4(r)	32.90–35.99
Walk only	2	40.4*†	38.98–41.88
Jog only	2	56.4*†	53.57–59.32
Gallop only	16	46.9*	42.73–51.03
Breeze/race	64	58.8*†	53.54–64.13

• * = significantly different (P < 0.05) from reference group (r). † = significantly different from prior category (P < 0.05).

Figure 1. Plasma GGT levels (U/L) by age (A), sex (B), raced vesus not raced (C), days since last race (D), maximum morning workload (E) and maximum workload in the previous week (F). Solid lines represent median values. Dashed lines represent the upper laboratory reference range (45 U/L).

University of California, Davis, Davis, CA, USA

Background: There is a need to evaluate the physiological effects of resuscitative fluids administered to sick neonatal foals admitted to intensive care units.

Hypothesis/Objectives: The hypothesis was that administration of isotonic replacement solutions would result in improvements in blood gas parameters in sick neonatal foals. We aimed to compare electrolytes, acid base variables and blood gas results pre- and post-fluid therapy.

Animals: 115 neonatal foals.

Methods: Retrospective study of sick neonatal foals that received isotonic replacement fluids upon admission to a neonatal ICU. Foals had measurement of venous blood gases and electrolytes before and after initial fluid therapy. Variables were compared using a Wilcoxon signed-rank test.

Results: The study included 115 foals. PlasmaLyte was administered to 92% of the foals. Significant decreases were found in the following analytes after fluid therapy: PCV, pre- and post-fluids (39[22–54] vs. 35[21–51%]; P < 0.0001); Total protein pre- and post-fluids (5.2[3.1–11.0] vs. 4.9[2.9–10.6 g/dL]; P < 0.0001); Lactate, pre- and post-fluids (3.4[0.8–25] vs. 2.6[0.6–16 mmol/L] P < 0.0001); AG, pre- and post-fluids (10.9[−1.4–37.1] vs. 10.5[−3.3–28.4] P = 0.002).

The following had significant increases after fluids: Sodium, pre- and post-fluids (137[109–161] vs. 137[112–158 mEq/L] P = 0.007); Bicarbonate, pre- and post-fluids (28.0[10.6–34.3] vs. 28.3[11.2–37.7 mEq/L] P < 0.0001); Base excess [BE] pre- and post-fluids (2.9[−18.6–9.5] vs. 3.5[−20.7–11.7] P < 0.0001); abbreviated strong ion difference (SID), pre- and post-fluids (35[14–53] vs. 36[16–52] P = 0.0003); Glucose, pre- and post-fluids (122[4–336] vs. 137[16–438 mg/dL] P = 0.0004).

Conclusions and Clinical Importance: Markers of hydration (PCV, TP) and metabolic acidosis (BE, bicarbonate, anion gap, SID, and lactate) improved with fluid therapy in ill neonatal foals.

¹Virginia-Maryland College of Veterinary Medicine, Blacksburg, VA, USA; ²Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Blacksburg, VA, USA; ³Large Animal Clinical Sciences, Virginia-Maryland College of Veterinary Medicine, Blacksburg, VA, USA

Background: Pimobendan is an inodilator approved for treatment of canine cardiac disease. The pharmacokinetics have not been investigated in horses.

Hypothesis/Objectives: This study evaluated the pharmacokinetics of oral Vetmedin (V) in horses. Additional objectives were to determine the bioequivalence of compounded pimobendan capsules (C) and suspension (S) and the effects of sample site on plasma drug concentrations.

Animals: Six privately-owned healthy adult horses (5 mares, 1 gelding).

Methods: All horses received a single 0.5 mg/kg dose of pimobendan via oral syringe. The initial two horses received C, S, or V using a crossover design with a minimum 1-week washout period. Samples were collected simultaneously from lateral thoracic and jugular catheters before and after drug administration at predetermined times. Differences between formulation and sample site were analyzed by one-way ANOVA. The remaining 4 horses received (V) only with jugular samples collected. Analysis was by LC-MS/MS and noncompartmental pharmacokinetics for (V).

Results: No significant differences were noted between formulations or sample site (p>0.05). Concentrations in compounded formulations were 90%(C) and 88%(S) of label. For V, mean (±SD) maximum plasma concentration (C_max) was 4.96 ± 2.13 ng/mL at 2.17 ± 0.98 hr, and area under the curve (AUC0–∞) was 22.1 ± 8.8 hr ng/mL. ODMP was not detected in any sample (<0.07 ng/mL).

Conclusions and Clinical Importance: At 0.5 mg/kg PO, pimobendan plasma concentrations were considerably lower than reported in dogs. There was no evidence of oral transmucosal absorption. Pimobendan is poorly absorbed in horses, regardless of formulation, and appears unlikely to have clinical effects.

¹Iowa State University, Ames, IA, USA; ²Department Chair, Veterinary Clinical Sciences, Iowa State University, Ames, IA, USA; ³Associate Professor, Pharmacology, Washington State University, Pullman, WA, USA; ⁴Professor, Pharmacology & Genomics, Washington State University, Pullman, WA, USA; ⁵Associate, Wisconsin Equine Clinic and Hospital, Summit, WI, USA

Background: Acetaminophen is used in infants for antipyresis and analgesia. Neonatal foals might benefit from acetaminophen therapy, but effective and safe dosages for foals are unknown.

Objectives: To determine the pharmacokinetics and clinical safety of acetaminophen following oral administration of 40 mg/kg q 12 h or 60 mg/kg q 24 h for 14 days.

Animals: Twelve healthy neonatal light-breed foals.

Methods: Foals received acetaminophen orally either at 40 mg/kg q 12 h or 60 mg/kg q 24 h for 14 days. Physical exams were performed daily. Plasma disposition of acetaminophen was determined after first and last drug administration and at the study midpoint. Hematology and serum chemistry analysis was performed prior to the study, at midpoint, and on the last day of administration. Plasma acetaminophen concentrations were determined by high performance liquid chromatography, and plasma pharmacokinetic parameters estimated using non-compartmental analysis.

Results: No statistically significant changes occurred on hematology and biochemistry profiles; elevations in GGT or SDH were seen in 4 foals at various timepoints. C_max occurred within 2 h for both doses. The 60 mg/kg dose resulted in a larger median C_max (range) at 28 mg/ml (22–32) than the 40 mg/kg dose at 23 mg/ml (19–27). The median AUC_{0–8 h} (range) was 100 h μg/mL (82–100) at 40 mg/kg and 128 h μg/mL (120–168) for 60 mg/kg. Trough concentrations decreased over time for both regimens.

Conclusions and Clinical Importance: Foals tolerate oral acetaminophen at 40 mg/kg q 12 h or 60 mg/kg q 24 h. Further analgesic and antipyretic studies will help to delineate optimal dosage regimens of acetaminophen to treat foals.

Table 1. Plasma pharmacokinetic parameters (median [range]) of acetaminophen estimated by noncompartmental analysis in foals after oral administration at 40 mg/kg of body weight every 12 h or 60 mg/kg of body weight every 24 h

PK parameter	Unit	40 mg/kg (n = 6)	60 mg/kg (n = 6)
Tmax	H	0.5 (0.5–1)	1 (0.5–2)
Cmax	μg/mL	23 (19–27)	28 (22–32)
AUC0–4h	H* μg/mL	64 (56–79)	83 (72–103)
AUC0–8h	H* μg/mL	100 (82–120)	128 (120–168)
Cmax/dose	N/a	0.58 (0.48–0.55)	0.46 (0.36–0.53)
CTrough—day 1	μg/mL	3.1 (1.5–6.6)	0.48 (0.2–1)
CTrough—day 7	μg/mL	1.6 (0.5–3.1)	0.26 (0.05–0.5)
CTrough—day 15	μg/mL	1.3 (0.4–2.6)	0.4 (0.17–0.6)

• AUC_0–4h and AUC_0–8h = area under the plasma concentration-time curve from 0, 4 and 8 h after the first drug administration; C_max = maximum concentration time to maximum concentration after the first administration; T_max = time to maximum concentration after the first administration. C_{Trough-day 1,7} corresponds to the plasma concentration before the next administration on the days indicated in the table. C_{Trough-day 15} corresponds to 12 and 24 h after the administration for the 40 mg/kg and 60 mg/kg, respectively. N/a = not applicable.

Figure 1. Plasma disposition of acetaminophen in 5–6 days old neonates. Panel A: plasma disposition after the first oral administration at 40 mg/kg (n = 6) or 60 mg/kg (n = 6). Panel B: Trough plasma concentration of acetaminophen at day 1, 7 and 15 following the administration of 40 mg/kg every 12 h or 60 mg/kg every 24 h.

¹University of Tennessee, Knoxville, TN, USA; ²Large Animal Clinical Sciences, University of Tennessee, Knoxville, TN, USA; ³College of Veterinary Medicine, Lincoln Memorial University, Harrogate, TN, USA; ⁴Biomedical and Diagnostic Sciences, University of Tennessee, Knoxville, TN, USA; ⁵Professor, Biomedical and Diagnostic Sciences, University of Tennessee, Knoxville, TN, USA

While oral omeprazole is a standard treatment for gastric ulcers in horses, an intravenous formulation is no longer commercially available in some areas. For horses unable to absorb orally administered omeprazole, intravenous esomeprazole, the s-enantiomer of omeprazole may be an option, but the pharmacokinetics of this drug in horses are currently unknown. Six healthy adult mares were administered a 0.5 mg/kg dose of esomeprazole intravenously and orally in a randomized crossover fashion. After administration, nineteen blood samples were taken over 24 h and repeated with the opposite treatment after a washout period. Samples were analyzed via HPLC for esomeprazole concentrations and time versus concentration data was modeled with standard industry software. The C0, T½, and AUC of IV administered esomeprazole was 2030 ng/mL, 24 min, and 660 ng/ml × h respectively. The C_max, T½, AUC, and F of oral esomeprazole was 104 ng/mL, 40 min, 114 ng/ml × hr and 25%. Clinicians should consider higher oral doses due to low bioavailability, and further research should focus on pharmacodynamic studies evaluating ulcer healing with esomeprazole therapy in horses.

Purdue University, West Lafayette, IN, USA

Background: In horses, the proportion of neutrophils in bronchoalveolar lavage (BAL) is related to dust exposure. Dietary intake of omega-3 polyunsaturated fatty acids also affects BAL neutrophil proportions, presumably due to changes in the concentrations of specialized pro-resolving lipid mediators (SPM).

Hypothesis/Objectives: Plasma SPM concentrations are related to BAL neutrophil proportions and modulate the relationship between dust exposure and neutrophils in the airway.

Animals: Twenty-five Thoroughbred racehorses housed at the local racetrack.

Methods: As part of a feed trial, BAL cytology, dust exposure (PM2.5), and plasma SPM (ELISA) were measured at week-0 and week-6. We used univariate generalized linear mixed models (GLMM) to screen for the effect of each SPM on BAL neutrophil proportions. Any SPM identified as significantly related to neutrophil proportions was included in a multivariate GLMM of BAL neutrophil proportions that also included dust exposure and the interaction between SPM and dust exposure as explanatory variables. Significance was set at P < 0.05.

Results: Plasma resolvin D2 (RvD2) concentration was significantly related to BAL neutrophil proportions (P = 0.0496). Multivariate analyses revealed a significant interaction between RvD2 concentration and PM2.5 exposure (P = 0.0052). At the mean PM2.5 exposure (0.01 mg/m³), a 50 pg/ml increase in the RvD2 concentration resulted in a 15% reduction in the BAL neutrophil proportion.

Conclusions and Clinical Importance: In the horse, plasma RvD2 dampens the neutrophilic response of the airway to dust exposure. Diets or supplements that increase plasma RvD2 concentration may be beneficial in the management of neutrophilic airway inflammation.

¹Université de Montréal, Montreal, QC, Canada; ²Full professor, Vice-Dean, Clinical Studies, Université de Montréal, Montreal, QC, Canada; ³Associate Professor, Clinical Studies, Université de Montréal, Montreal, QC, Canada

Background: Altered innervation structure and function contributes to airway hyperresponsiveness in humans with asthma. However, the morphology of equine airway innervation and its contribution to airflow limitation in equine asthma remains largely unknown.

Hypothesis/Objectives: To characterize peribronchial innervation in horses with asthma. We hypothesized that peribronchial nerve density increases in horses with asthma compared to controls.

Animals: Formalin-fixed lung samples from eight horses with severe asthma (five in exacerbation, three in remission) and eight controls. Lung function had been recorded prior to sample collection.

METHOS: Blinded case-control study. Immunohistochemistry was performed using rabbit anti-s100 antibody as a neuronal marker for myelinating and non-myelinating Schwann cells. Using histomorphometry, the number and the area of nerves in the peribronchial space and in proximity to airway smooth muscle were recorded and corrected for airway size.

Results: Both the number and the area of peripheral nerves were increased in the peribronchial region of horses with asthma (median (range): 1.87 × 10⁻⁵ nerves/μm² (6.25 × 10⁻⁶ to 6.29 × 10⁻⁵) and 1.03 × 10⁻³ nerve area/μm2 (5.40 × 10⁻⁴ to 2.38 × 10⁻³)) compared to controls (5.17 × 10⁻⁶ nerves/μm² (2.37 × 10⁻⁶ to 1.94 × 10⁻⁵) and 4.14 × 10⁻⁴ nerve area/μm² (1.08 × 10⁻⁴ to 1.61 × 10⁻³)) (Mann-Whitney, P < 0.01). The number of nerves within or surrounding airway smooth muscle was significantly increased in horses with asthma (4.47 × 10⁻⁶ nerves/uum2 (2.10 × 10⁻⁶ to 2.73 × 10⁻⁵)) compared to controls (2.26 × 10⁻⁶ nerves/μm2 (4.60 × 10⁻⁷ to 1.07 × 10⁻⁵)) (Mann-Whitney, P < 0.05). Airway innervation in horses in exacerbation was not correlated with resistance or elastance (Spearman's correlation: r < 0.35, P > 0.50).

Conclusions and Clinical Importance: Equine asthma is associated with increased airway innervation, which may contribute to airway smooth muscle remodeling and asthma severity.

¹College of Veterinary Medicine, Purdue University, West Lafayette, IN, USA; ²Research Scientist, Veterinary Clinical Scientist, Purdue University, West Lafayette, IN, USA; ³Research Technologist, Veterinary Clinical Sciences, Purdue University; ⁴Equine Medical Center, Cypress, CA, USA; ⁵Teigland, Franklin and Brokken, Fort Lauderdale, FL, USA; ⁶Equine Sports Medicine and Surgery, Weatherford, TX, USA; ⁷Associate Professor, Nutrition Science, Purdue University, West Lafayette, IN, USA; ⁸Professor, Occupational and Environmental Health, University of Iowa, Iowa City, IA, USA; ⁹Assistant Professor, Occupational Health and Environmental Health Sciences, Purdue University, West Lafayette, IN, USA

Background: When combined with low dust diets, omega-3 polyunsaturated fatty acids (ω-3) supplementation can reduce neutrophil proportions in the bronchoalveolar lavage fluid (BAL) of horses with asthma and healthy horses. It is unknown if ω-3 supplementation is effective without concurrent dust mitigation.

Hypothesis/Objectives: Dietary supplementation with fish oil rich in ω-3 will lower the proportion of neutrophils in BAL of horses fed a conventional diet including hay.

Animals: Clinically healthy racing Thoroughbreds (55) housed at 4 US racetracks.

Methods: In this double-masked controlled trial, horses were randomly assigned to receive daily fish oil (50 mL) or placebo (corn oil) for 4 weeks. Exposures of particulate matter smaller than 10 μm (PM10) were measured and BAL was collected at baseline and after 4 weeks of supplementation. The effects of supplementation on BAL neutrophil proportions and the relationship with PM10 exposure were evaluated using a generalized linear model. Significance was set at P < 0.05.

Results: BAL neutrophils decreased from 7.8 ± 0.01% to 5.3 ± 0.01% (mean ± s.e.m.) in horses given fish oil compared to placebo (5.9 ± 0.01% to 9.3 ± 0.02%; P = 0.029). After 4 weeks of fish oil supplementation, PM10 exposure was not related to BAL neutrophils (P = 0.2) but after placebo supplementation, PM10 exposure was related to BAL neutrophils (P < 0.0001), with a 10 μg/m³ increase in PM10 from the mean exposure resulting in a 1.3-fold increase in BAL neutrophils.

Conclusions and Clinical Importance: Supplementation with fish oil reduces BAL neutrophil proportions in clinically healthy racehorses independent of dust exposure. Increasing ω-3 intake might help mitigate neutrophilic asthma in horses.

Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA

Background: Hemosiderophages in bronchoalveolar (BAL) cytology are commonly ascribed to exercise-induced pulmonary hemorrhage (EIPH); little information exists regarding the presence of these cells in horses that perform light or no work and referred for respiratory evaluation.

Objectives: To evaluate the presence of and predictors for hemosiderophages in BAL cytology of horses suspected of respiratory disease without history of or risk factors for EIPH.

Animals: BAL cytologies of 353 horses evaluated for respiratory disease between 2012 and 2022 at a referral center were retrospectively reviewed.

Methods: This was an observational retrospective cross-sectional study. Horses with a history or likelihood of past strenuous exercise were removed; the remaining 91 were classified as hemosiderin-positive (HSD-POS) or hemosiderin-negative (HSD-NEG) based on Prussian Blue staining. Potential predictors of the presence of hemosiderophages (history, clinical evaluation, baseline lung function, airway reactivity, BAL cytology and hemosiderin score) were compared between the two groups, using univariate and multivariate analyses.

Results: Horses with a diagnosis of severe equine asthma were significantly more likely to be HSD-POS than horses with mild-moderate equine asthma (odds ratio 11.1 (95% confidence interval [3.2–38.5]), P < 0.001).

Conclusions and Clinical Importance: Hemosiderophages were found in the BAL cytology in a subset of horses that perform light or no work and presenting for respiratory evaluation. The link between hemosiderophages and severe equine asthma may help elucidate previously unstudied pathology associated with equine asthma.

¹New Bolton Center, University of Pennsylvania, Kennett Square, PA, USA; ²Metabolomics Core, Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA; ³Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN, USA; ⁴Department of Biomedical & Diagnostic Sciences, College of Veterinary Medicine, University of Tennessee; ⁵Department of Clinical Sciences and Advanced Medicine, College of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA, USA

Background: Metabolomics studies have been performed in limited studies of horses with asthma with varying results. In this study, mass spectrometry-based metabolomics was used to profile BALF from horses to identify metabolites related to the pathogenesis of this disease.

Hypothesis/Objectives: We hypothesized that horses with asthma would have significant differences in metabolic profiles of BALF supernatant versus healthy. Our objective was to utilize untargeted LC/MS metabolomics to identify biomarkers in suspect asthmatic horses.

Animals: Institution-owned, and client-owned horses were enrolled. Five healthy and 5 suspect asthma horses were included.

Methods: BALF was collected from horses with suspect asthma during active disease and supernatant stored at −80°C. Metabolites were extracted from BALF in ice cold methanol and separated using reversed-phase C18 and HILIC chromatography coupled to a Thermo Vanquish UHPLC/Orbitrap ID-X mass spectrometer. Compound Discoverer (Thermo Scientific) was used to process raw mass spectrometry data and perform a metabolite database search. Metabolites having a Welch's t-test P value <0.05 with Benjamini-Hochberg correction were considered. Post-processing involved generation of principal component analysis (PCA) plot, volcano plot, box-and-whisker plots, and heat maps.

Results: Several metabolites were identified in BALF including some that were important for group clustering and separation. Two metabolites identified that are potentially interesting in relation to airway disease are N-acetylserotonin and N-tetradecanoylsphinganine.

Conclusions and Clinical Importance: Identification of potential significant metabolites in horse BALF was possible utilizing LS/MS metabolomics, which may improve our understanding of equine asthma pathophysiology in follow-up studies.

¹University of Pennsylvania New Bolton Center, Kennett Square, PA, USA; ²Diagnostic Imaging, University of Pennsylvania New Bolton Center, Kennett Square, PA, USA

Background: Congestive heart failure (CHF) in goats is poorly described but increasingly diagnosed as pet goats become more popular. More information on caprine cardiac disease is warranted.

Hypothesis/Objectives: This retrospective study aimed to describe presentation, clinical findings, treatment, and outcome of goats diagnosed with CHF.

Animals: Medical records of goats admitted to a tertiary referral center from 2008–2022 were reviewed.

Methods: Goats were included if diagnosed with CHF. Clinical findings, diagnosis, treatment, and survival were recorded. Fisher's exact tests were performed to assess for association between clinical findings and survival.

Results: Twelve cases met inclusion criteria, 58% presented for anorexia/weight loss. Findings included tachycardia (92%), effusion (92%), elevated GGT (92%), low or inappropriately normal fibrinogen given disease severity (58%), tachypnea (58%), a murmur (25%), arrhythmia (17%), edema (25%), cough (25%), and jugular pulses (8%). There was no association between these findings and survival (P ≥ 0.05). All 12 were diagnosed with right-sided CHF, 9 had primary cardiac disease. 33% were euthanized shortly after presentation, 33% died or were euthanized after some treatment and 33% survived. Cardiac medications included beta blockers (n = 2), digoxin (n = 1), benazepril (n = 1), and furosemide (n = 4). One goat received transcutaneous electrical cardioversion (TCEC) of atrial fibrillation. Sixty percent of the goats that received cardiac targeted treatment survived to discharge.

Conclusions: CHF should be considered in goats presenting with weight loss, tachycardia, effusions, and biochemical values consistent with hepatic dysfunction. Although not previously reported TCEC and medical management are possible. Further research is needed to better understand CHF in goats.

University of Montreal, Montréal, QC, Canada

Background: Conditions that present as abdominal emergencies in dairy cattle are frequent. Decisions regarding diagnostic and treatment are challenging. Prognosis remains difficult to estimate.

Hypothesis/Objectives: Describe the clinical presentation and outcome of abdominal emergencies in dairy cows admitted to a referral hospital.

Methods: Retrospective study. Review of medical records of dairy cows admitted between 2016 and 2021 for an abdominal emergency. Definition included: decreased or absent fecal production and/or visceral or parietal pain and duration of less than 7 days. Data regarding history, physical examination, blood work, treatment, diagnosis, and outcome were studied. Descriptive statistics were performed.

Results: Two hundred and thirty-seven cows were enrolled. Fifty-eight percent (129/222) were in the first 3 months of lactation. The most common clinical signs were dehydration (65%, 155/237), decrease or absence of feces (62%, 146/237), tachycardia (54%, 128/237), and parietal pain (41%, 96/237). A median lactate of 4.3 mmol/L, chloride of 95 mmol/L, and ionized calcium of 1.06 mmol/L were present at admission. Of the cows that were treated, 53% (125/226) underwent surgery. Final diagnosis consisted of small intestinal disorders (32%, 76/237), peritonitis (27%, 63/237), abomasal disorders (25%, 60/237), large intestinal disorders (5%, 13/237), and others (10%, 25/237). Sixty-nine percent of the admitted cattle were discharged from the hospital, 45% and 40% were alive after 2 and 6 months, respectively.

Conclusions and Clinical Importance: The majority of cows were in early lactation. Abdominal pain was predominantly parietal. About half of the cases were treated only medically. The overall prognosis was fair.

¹Cornell University, Ithaca, NY, USA; ²Associated Professor, Population Medicine, University of Guelph, Guelph, ON, Canada; ³PhD student, Population Medicine, University of Guelph, Guelph, ON, Canada; ⁴MSc Student, Clinical Studies, University of Guelph, Guelph, ON, Canada; ⁵Assistant Professor, Universite de Montreal, Montreal, QC, Canada; ⁶Assistant Professor, Population Health and Pathobiology, North Carolina State University, Raleigh, NC, USA; ⁷Assistant Professor, Clinical Studies, University of Guelph, Guelph, ON, Canada

Background: Fecal samples for microbiota studies in calves are usually collected on a weekly basis. This approach can result in collection of samples from diarrheic calves without considering the time of diarrhea onset.

Objective: Compare the fecal microbiota of healthy calves, calves with diarrhea onset on the day of sampling (D < 24 h), and calves having diarrhea for >24 to 48 h (D 24–48 h).

Animals: 20 healthy, 20 D < 24 h, and 11 D 24–48 h veal calves of 3–7 days of age.

Methods: Case control study. Calves with loose or watery feces were considered as diarrheic. Fecal samples were collected on day 7 after arrival on farm. Fecal microbiota was characterized by sequencing of 16S ribosomal RNA gene amplicons.

Results: The fecal community membership (Jaccard index) and structure (Yue & Clayton index) of healthy calves were significantly different than those of diarrheic calves (AMOVA, P < 0.001 for both comparisons). Both the bacterial membership and structure differed significantly between D < 24 h and D 24–48 h calves (AMOVA, P < 0.001 for both comparisons). Phocaeicola, Bacteroides, Prevotella, Faecalibacterium, Butyricicoccus, Ruminococcaceae, and Lachnospiraceae were enriched in healthy calves. Enterococcus, Ligilactobacillus, Lactobacillus, and Gallibacterium were enriched in the feces of D<24 h calves, while Enterococcus, Streptococcus, Clostridium sensu stricto and Escherichia/Shigella were enriched in the D 24–48 h calves.

Conclusions: Rapid changes in fecal microbiota occur during the first 48 h of diarrhea. The time from diarrhea onset to sampling affect the bacterial composition of feces of diarrheic calves. Researchers should standardize times for fecal collection based on the time of diarrhea onset rather than convenient times.

¹Veterinary Medical Teaching Hospital, University of California Davis, Davis, CA, USA; ²Professor, Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California Davis, Davis, CA, USA

Background: Transfusion with fresh frozen plasma (FFP) or hetastarch 6% (HES) are indicated for management of decreased colloid oncotic pressure (COP) in hypoproteinemic calves. However, HES has been associated with coagulopathies in other species. The effectiveness of HES compared to FFP has not been extensively studied in calves.

HYPOTHESES: Administration of HES increases COP to levels comparable to FFP. The administration of HES does not alter coagulation parameters.

Animals: 7 dairy bull calves from a university teaching herd.

Methods: Cohort, clinical trial in 2-way crossover design, with a 2-week washout period. HES and FFP were administered intravenously at 10 and 20 mL/kg, respectively, once. Serum COP was measured pre-transfusion, and at 0, 1, 2, 4, 6, 12, 24, 36, and 72 h and 7 days after each transfusion. Coagulation parameters including prothrombin time, partial thromboplastin time, fibrinogen, fibrinogen degradation products and thrombocytes analysis were performed pre-transfusion, and at 0, 24, and 72 h after transfusion. Effect of treatment and time on COP and coagulation parameters was determined by MANOVA.

Results: Transfusion with HES or FFP was positively associated with serum COP. Time did not have an effect on COP. Administration of FFP or HES did not significantly change (P > 0.05) the coagulation parameters.

Conclusions and Clinical Importance: HES is an effective alternative to FFP transfusion in calves, and it does not cause significant changes in coagulation parameters.

¹College of Veterinary Medicine, Chungbuk National University, Cheongju, South Korea; ²Laboratory of Veterinary Internal Medicine, College of Veterinary Medicine, Chungbuk National University, Cheongju, South Korea

Background: Fucoidan which is sulfated polysaccharide extracted from brown seaweed has a wide variety of biological activities. Neutrophil extracellular traps (NETs) formation is an immune response for the invasion of microbes. Neutrophils release granule protein and chromatin that together form extracellular fibers that bind pathogens.

Hypothesis/Objectives: To examine the effect of fucoidan on NET formation of porcine peripheral blood polymorphonuclear cells (PMNs).

Animals: Clinically healthy 6-month-old pigs were included as donors for peripheral blood mononuclear cells (PBMCs).

Methods: The NET formation was measured by fluorescence microplate reader. The production of tumor necrosis factor (TNF)-α in the culture supernatants from peripheral blood mononuclear cells (PBMCs) was measured by ELISA method.

Results: Fucoidan itself did not cause any direct effect on NET formation. However, NET formation of PMNs were increased by the culture supernatant from PBMCs treated with fucoidan. The NET formation of PMNs were also enhanced by treatment with recombinant porcine (rp) TNF-α. The ability of the culture supernatant from fucoidan treated PBMCs to stimulate the NET formation on porcine PMNs was inhibited by addition of goat anti-rp TNF-α polyclonal antibody (pAb; IgG) prior to the culture. NET formation of rp TNF-α was also suppressed by goat anti-rp TNF-α pAb. The level of TNF-α in culture supernatant from PBMCs was increased by treatment with fucoidan.

Conclusion and Clinical Importance: These results suggested that fucoidan has an immunoenhancing effect on the NET formation of porcine PMNs, which is mediated by TNF-α released from fucoidan-treated PBMCs.

¹Large Animal Teaching Hospital, Auburn University, Auburn, AL, USA; ²Professor, Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, AL, USA; ³Ireland Professor, Forestry and Wildlife Sciences, Auburn University, Auburn, AL, USA; ⁴Biologist, National Feral Swine Damage Management Program, USDA/APHIS/Wildlife Services; ⁵Lab Tech III, Animal Health and Disease Research, College of Veterinary Medicine, Auburn University, Auburn, AL, USA; ⁶Associate Professor, Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, AL, USA; ⁷Professor and Head, Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL, USA; ⁸Associate Professor, Coordinator, Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL, USA; ⁹Assistant Professor, Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL, USA

Background: Wild pigs are a reservoir for numerous infectious diseases, many of which are zoonotic or of concern to other species. Bovine viral diarrhea virus (BVDV) represents a major disease of economic concern for the livestock industry. Infections in swine typically do not result overt disease but may spill-back into cattle and other ruminants.

Hypothesis/Objective: The first objective was to determine the seroprevalence of BVDV in wild pigs by comparative serology. The second objective was to determine if state, age category, or sex significantly affected serum neutralization titers.

Animals: A total of 1129 serum samples from wild pigs were collected across 17 states.

Methods: The samples underwent an initial virus neutralization (VN) assay at a dilution of 1:2 to screen for the presence of neutralizing antibodies or cytotoxicity. For positive samples, serial 2-fold dilutions starting at 1:2 with a final dilution of 1:65 536 was performed to determine end point titers. All samples underwent comparative serology to both BVDV-1b strain TGAC and BVDV-2a strain 125-c.

Results: Sixty-seven samples were excluded from analysis due to cytotoxicity. Thirty-nine samples were positive to BVDV-1b. Thirty-two samples were positive to BVDV-2a. Overall prevalence for BVDV-1b was 4.4% and 3.6% for BVDV-2a, respectively. The prevalence among the different states varied from 0% to 16.7%.

Conclusions and Clinical Importance: The seroprevalence was determined to be similar to previously reported results for wild pigs in other countries. Age category and sex did not significantly affect serum neutralization titers, nor were risk factors for having a positive antibody titer.

¹Ghent University, Ghent, Belgium; ²Doctor, Department of Pathobiology, Pharmacology and Zoological Medicine, Ghent University, Ghent, Belgium; ³Department of Internal Medicine, Reproduction and Population Medicine, Ghent University, Ghent, Belgium; ⁴Professor, Department of Internal Medicine, Reproduction and Population Medicine, Ghent University, Ghent, Belgium; ⁵Post-Doc, Department of Internal Medicine, Reproduction and Population Medicine, Ghent University, Ghent, Belgium

Background: Sepsis is a life-threatening condition for which critically important antimicrobials are often indicated. The value of blood culture for sepsis is indisputable, but appropriate sampling guidelines are lacking in calves.

Objectives: To compare diagnostic accuracy and time to positivity (TTP) of two blood culture media (pediatric plus [PP] and plus aerobic [PA]), with a different volume (3 vs. 10 mL) and composition. To estimate blood culture contamination in calves.

Animals: 126 critically ill calves.

Methods: Diagnostic test study in which performance of PP, PA, and hypoglycemia (<60 mg/dL) was assessed to detect sepsis using a Bayesian latent class model. Survival analysis was used to compare TTP. Contamination was descriptively analyzed. Pathogens were considered relevant when: (1) member of the Enterobacteriaceae family, (2) highly relevant in other bovine pathologies, or (3) isolated from both blood cultures.

Results: The sensitivities for PP, PA, and hypoglycemia were 68.7% (95% credibility interval = 30.5%–93.7%), 87.5% (47.0%–99.5%) and 61.3% (49.7%–72.4%), respectively. Specificity was estimated at 95.1% (82.2%–99.7%), 94.2% (80.7%–99.7%) and 72.4% (64.6%–79.6%). No significant difference in TTP was identified between PP and PA. An overall contamination rate of 8.3% (21/252) was assumed, and blood culture positivity reduced (40.5% to 22.2%) when presumed contaminants were excluded.

Conclusions and Clinical Importance: The PA culture seems to have the highest diagnostic test accuracy compared to PP and hypoglycemia, and the type of culture did not influence TTP or the contamination rate. Therefore, sampling PA culture twice is theoretically the best option to determine sepsis in critically ill calves.

¹Mississippi State University, Mississippi State, MS, USA; ²Assistant Clinical Professor, Pathobiology and Population Medicine, Mississippi State University, Mississippi State, MS, USA; ³Professor, Comparative Biomedical Sciences, Mississippi State University, Mississippi State, MS, USA

Background: Urinary acidification with ammonium chloride (NH₄Cl) for urolith dissolution is a common treatment for goats with urolithiasis. Studies have reported increased fractional excretion of calcium (FECa) following NH₄Cl administration, which could increase calcium-based urolithiasis. D,L methionine may result in similar acidification with less calcium excretion.

Objectives: To compare effects of orally administered D,L methionine and NH4Cl on urine and blood pH, FECa, and blood HCO3− concentrations in male goats.

Animals: Twelve healthy 4–6-month-old Boer-cross wethers.

Methods: Prospective, randomized, cross over study. Wethers were administered 200 mg/kg of NH₄Cl or D,L methionine orally for 14 days with a 7 day washout period between trials. Venous blood and urine samples were collected every 2 days. The effects of treatment and treatment day on urine and blood pH, FECa, and HCO3- was assessed using linear mixed models.

Results: In models with treatment and day, mean urine pH on day 6 (μ = 7.49, P < 0.001), 8 (μ = 7.78, P = 0.008, and 10 (μ = 7.53, P < 0.001) was significantly lower than on day 0 (μ = 8.23). A significant treatment effect was not detected on urine pH (P = 0.1158), blood pH (P = 0.7683), FECa (P = 0.4038), and blood HCO3- (P = 0.1422).

Conclusion and Clinical Importance: Urine pH was decreased on days 6, 8, and 10, however, values were not low enough to dissolve uroliths. Under the conditions of this study, there was no difference in FECa between treatments. Further studies should investigate effects of higher doses of these drugs.

¹Food Animal Medicine Resident, North Carolina State University, Raleigh, NC, USA; ²Assistant Professor, North Carolina State University, Raleigh, NC, USA; ³Assistant Professor, Ruminant Medicine, North Carolina State University, Raleigh, NC, USA; ⁴Food Animal Intern, North Carolina State University, Raleigh, NC, USA

Background: Obstructive urolithiasis (OU) is a common small ruminant emergency and can lead to hydronephrosis and intrinsic renal disease. As post-renal azotemia is common in goats with OU, diagnosis of intrinsic renal disease prior to surgical correction of OU is challenging. Symmetric dimethylarginine (SDMA) is a renal biomarker correlated with early detection of renal disease. SDMA has not been validated in goats.

Hypothesis/Objectives: The objectives of this study are to establish reference ranges for SDMA in healthy goats and describe changes in SDMA in goats with OU.

Animals: Healthy goats, both male and female, from a research herd (n = 59). Goats with clinical OU (n = 12).

Methods: Healthy goats had blood collected at a single time point. Clinically affected goats had blood collected at presentation, 24, 48 and 72 h post-surgery for SDMA and biochemistry analysis. Urine was collected for urinalysis at presentation. Descriptive statistics will be used to assess values in both the healthy and obstructed goat populations.

Results: For the healthy group, the mean SDMA value was 17.6 μg/dL, median SDMA value of 17 μg/dL and a range of 7 to 43 μg/dL. Currently, eight goats with obstructive urolithiasis have samples collected. Analysis will be conducted once the sample size has been achieved.

Conclusions and Clinical Importance: SDMA has the potential to be used in clinical cases of caprine OU to provide prognostic information prior to surgery.

¹College of Veterinary Medicine, Auburn University, Auburn, AL, USA; ²College of Veterinary Medicine, Kansas State University, Manhattan, KS, USA; ³Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, AL, USA; ⁴Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL, USA

Background: Diagnosis and treatment of non-ambulatory beef cattle are challenging, and scientific reports of prognostic indicators for survival in downer beef cattle are unavailable.

Hypothesis/Objectives: To evaluate records of downer adult (≥2 years of age) beef cattle presented to two referral hospitals to identify prognostic indicators for survival to discharge.

Animals: Sixty-three recumbent beef cattle.

Methods: Retrospective case study. Medical records of beef cattle presented to two referral hospitals for recumbency (inability to stand) between 2010 and 2022 were analyzed. Univariable and multivariable logistic regression analyses were performed to evaluate the associations of predictors with survival to discharge.

Results: Of 63 cattle included, 51 (81%) died or were euthanized and 12 (19%) survived to discharge. Cattle not receiving float tank therapy (OR = 4.11), those with neutrophilia (OR = 10.67) or with hyperglobulinemia (OR = 2.77) at presentation had lower odds of survival to discharge. Cattle diagnosed with musculoskeletal disease including spinal/vertebral disease had lower odds (OR = 5.33) of survival to discharge compared to cattle diagnosed with peripheral nerve paralysis.

Conclusions: Recumbency is associated with a poor prognosis for survival to discharge in beef cattle. Float tank therapy may improve survival to discharge in some cases.

Southeast Veterinary Neurology of Boynton Beach, Boynton Beach, FL, USA

Background: Midazolam is frequently used for management of status epilepticus or cluster seizures at home. There are currently no studies looking at the stability of midazolam in the home environment.

Objective: The aim of this prospective study was to evaluate the degradation of midazolam over the course of 360 days in a simulated home environment using three different storage methods (light-protected glass vial [group A], light-protected syringe [group B] and non-light-protected syringe [group C]).

Methods: The concentration of midazolam was determined using high-performance liquid chromatography (HPLC) in triplicate, at each of the time points (0, 14, 30, 60, 120, 180, 270, and 360 days). A two-way ANOVA using Tukey's procedure was used to compare each storage environment at each time point.

Results: By 360 days, the midazolam concentration revealed an increase from the starting concentration. The mean concentration for group A, B, and C was 79.9%, 102.0%, and 107.0%, respectively, of the labeled concentration at day 360. The increase in concentration was not statistically significant between groups B and C, but was statistically significant between groups A and B and groups A and C.

Conclusions: This study demonstrated that dispensing ready-made syringes would be appropriate in order to facilitate ease of use and to expedite rescue therapy for epileptic dogs at home.

¹Washington State University, Pullman, WA, USA; ²Associate Professor (Neurology & Neurosurgery), Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, WA, USA; ³Assistant Professor, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, WA, USA; ⁴Assistant Professor, Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California - Davis, Davis, CA, USA; ⁵Assistant Professor, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, WA, USA

Background: Primary spinal cord injury (SCI) due to intervertebral disc extrusion (IVDE) is treated by surgical decompression, but no proven treatments exist for secondary SCI. N-acetylcysteine (NAC), a free radical scavenger, may reduce secondary SCI.

Hypothesis: Postoperative administration of NAC results in faster ambulation and reduced secondary SCI, as measured by serum phosphorylated neurofilament (pNF-H) and urinary 15F2t-isoprostane:creatinine (ISO).

Animals: 21 client-owned dogs with thoracolumbar IVDE.

Methods: Randomized, blinded, placebo-controlled trial. Dogs received intravenous NAC or placebo (0.9% saline) over 48 h postoperatively. Daily neurological examinations were performed. Serum and urine samples were collected before (t0) and after treatment (t48). pNF-H and ISO concentrations were quantified by ELISA and time to ambulation estimated. Outcome measures were compared within and between groups using Wilcoxon matched-pairs signed rank and Mann-Whitney U tests and paired/unpaired t-tests.

Results: pNF-H significantly increased over time in both the NAC [t0: 0.31 (0.00–1.12) ng/mL; t48: 1.67 (0.00–38.23) ng/mL, P = 0.01] and placebo group [t0: 0.12 (0.00–13.09) ng/mL; t48: 1.34 (0.00–41.33) ng/mL, P = 0.008]. ISO significantly increased in the NAC [t0: 728.1 ± 186.5 pg/mg; t48: 978.6 ± 215.9 pg/mg, P = 0.004] but not placebo group [t0: 1103.0 ± 334.1 pg/mg; t48: 1104.0 ± 435.9 pg/mg, P = 0.69]. No significant differences in pNF-H (P = 0.96) or ISO concentrations (P = 0.41) were found between groups at t48. Mean time to ambulation was not significantly different between groups [NAC: 15.6 ± 12.2 days; placebo: 9.5 ± 7.6 days, P = 0.31]. No adverse reactions were observed.

Conclusions and Clinical Importance: While well tolerated, NAC did not significantly reduce time to ambulation or secondary SCI.

¹Cornell University, Ithaca, NY, USA; ²Neurology/Neurosurgery, Cornell University, Ithaca, NY, USA; ³Adjunct Professor, Department of Clinical Sciences, Cornell University, Ithaca, NY, USA

Background: Clinical characteristics of cervical hydrated nucleus pulposus extrusion (HNPE) in canines compared to other causes of cervical myelopathy are not well described.

Hypothesis/Objectives: HNPE dogs will have specific clinical characteristics allowing differentiation compared to intervertebral disc extrusion (IVDE) and fibrocartilaginous embolism (FCE).

Animals: 268 client-owned dogs (46 HNPE, 192 IVDE, 30 FCE) presented to a neurology service from 2010 to 2022.

Methods: Retrospective study. Patients diagnosed with HNPE, IVDE, or FCE on MRI were included. Age, weight, pain score, Modified Frankel Score, and lateralizing signs were included for logistic regression. Central cord signs, disc space involvement, and ventilation requirement were evaluated separately.

Results: In a multinomial model (HNPE vs. IVDE, and HNPE vs. FCE), decreasing age modestly decreased the odds of HNPE (OR: 0.98 and 0.96), decreasing weight modestly increased the odds of HNPE (OR: 1.03 and 1.01). Increasing pain score increased the odds of IVDE (vs. HNPE; OR:2.05); while decreasing pain score increased the odds of FCE (vs. HNPE; OR: 0.42). Lateralization dramatically increased the odds of either IVDE or FCE (vs. HNPE; OR:2.3 and 7.3, respectively). 35% (16/46) of HNPE dogs had central cord signs, compared to 19% (36/192) IVDE and 13% (4/30) FCE. 70% of HNPE dogs had a lesion at C3-4 or C4-5. Ventilation was required for 9% HNPE, 1% IVDE, and 0 FCE cases.

Conclusions and Clinical Importance: Compared to IVDE and FCE, HNPE dogs have differences in clinical characteristics, and might be more likely to require ventilation. These differences should be considered for case management.

¹University of California Davis, Davis, CA, USA; ²Associate Project Scientist, Surgical & Radiological Sciences, VMTH, University of California, Davis, Davis, CA, USA; ³Academic Program Mgmt. Ofc., Comprehensive Cancer Center, University of California, Davis, Davis, CA, USA; ⁴Professor Neurology/Neurosurgery, Department of Surgical & Radiological Sciences, Veterinary Medical Teaching Hospital, University of California, Davis, CA, USA; ⁵Professor and Director, Cancer and Cell Biology Division, The Translational Genomics Research Institute, Phoenix, AZ, USA; ⁶Associate Professor, Department of Pathology, Microbiology and Immunology, University of California, Davis, Davis, CA, USA; ⁷Professor of Neurological Surgery, Neurosurgeon-in-Chief, Northwestern Medicine Program Leader, Neuro-Oncology, Department of Neurological Surgery, Lou and Jean Malnati Brain Tumor Institute, Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA; ⁸Assistant Professor, Department of Neurological Surgery, Lou and Jean Malnati Brain Tumor Institute, Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA; ⁹Assistant Professor, Department of Surgical and Radiological Sciences, VMTH, University of California, Davis, Davis, CA, USA

Animals: Four healthy dogs.

Methods: In vitro, mechanistic study. Canine Tregs were characterized by flow cytometry using canonical markers CD3, CD4, CD25, FOXP3, and CCR4 and sorted using fluorescent-activated cell sorting. CCL2 mRNA expression was assessed via RTqPCR in four canine glioma cell lines (1110, 0514, J3T-Bg, G06A). Treg migratory capacities were assessed using a Boyden chamber assay. Anti-CCL2 antibody and a CCR4 inhibitor (C021) were used in abrogation studies.

Results: The canine CD4+CD25high T-cell population expressed canonical Treg markers FOXP3 and CCR4. Canine Treg migration was enhanced by CCL2 and glioma cell line-derived supernatant. Blockade of the CCL2/CCR4 axis abrogated migration of Tregs. CCL2 mRNA was expressed in all cell lines and expression increased when exposed to Tregs but not to conventional CD4+ T-cells.

Conclusion: CD25high expression is critical for isolation of canine Tregs. Our study validated CCL2/CCR4 as a bi-directional Treg-glioma signaling axis and represents a rational target for immunotherapy in clinical patients.

¹College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA; ²The Ohio State University, Columbus, OH, USA; ³Associate Professor, The Ohio State University, Columbus, OH, USA

Background: Degenerative lumbosacral stenosis (DLSS) shows poor correlation between imaging and clinical findings in dogs. Kinematic or dynamic imaging may improve elucidation of this relationship. Kinematic MR imaging has not been evaluated in dogs with DLSS.

Objectives: Describe the morphologic features of the lumbosacral vertebral column of large-breed dogs with or without DLSS in neutral, flexed, and extended MRI positions.

Animals: 27 large-breed dogs: 15 DLSS-affected, and 12 clinically normal.

Methods: Prospective blinded morphologic study. Patients underwent a 3.0 T MRI in lateral recumbency (mimicking natural standing position), followed by imaging in flexed and extended positions using a kinematic positioning device. Eight morphologic parameters were assessed in each position, including Pfirrmann grade of discs, direction and cause of compression, presence/severity of foraminal stenosis, and percentage reduction in vertebral canal height.

Results: The lumbosacral angle was significantly different between the three positions (neutral, extension, and flexion) in both groups (P < 0.05). In neutral position, 15 compressions (counting both ventral and dorsal) were identified at the L7-S1 region in DLSS dogs, with nine in the normal group. In extension, there were 20 compressions in DLSS dogs, with 14 in the normal group. There were fewer compressions in flexion in both groups. There was a significant difference in vertebral canal height between neutral and extension (P < 0.05) and neutral and flexion (P < 0.05) in the DLSS group.

Conclusions: Kinematic MRI is a feasible technique for evaluation of the lumbosacral region. It can exacerbate existing compressive lesions and reveal new compressions not identified with neutral positioning alone.

¹Colorado State University, Ft Collins, CO, USA; ²Veterinary Student, Colorado State University, Ft Collins, CO, USA; ³Professor, Colorado State University, Ft Collins, CO, USA; ⁴Neurology Clinical Trials Coordinator, Colorado State University, Ft Collins, CO, USA; ⁵Associate Professor, Neurology, Colorado State University, Ft Collins, CO, USA

Background: Approximately 30% of dogs with idiopathic epilepsy are refractory to treatment. Recent studies have suggested cannabidiol (CBD) is an effective anticonvulsant in dogs with idiopathic epilepsy but more evidence is required.

Objective: Evaluate the effect of adding CBD to conventional antiepileptic drugs on seizure control and to report adverse events in dogs with idiopathic epilepsy.

Animals: 51 client-owned dogs diagnosed with idiopathic epilepsy were included in this study. Inclusion criteria required at least two seizures per month documented for 3 months preceding the trial.

Methods: This was a double-blinded, placebo-controlled crossover clinical trial. Twelve dogs were administered 5 mg/kg/day oral CBD, and 39 dogs were administered 9 mg/kg/day oral CBD. Dogs were randomly assigned to receive either CBD or placebo for 3 months then switched to the opposite oil for 3 months following a one-month washout period. Total number of seizures and seizure days (clusters over a 24-h period) were recorded. Blood work was performed periodically.

Results: At the 9 mg/kg/day dose, there was a decrease in number of total seizures during CBD treatment compared to placebo (P = 0.036). There was a significant reduction in seizure days (−24.1%) for dogs receiving 9 mg/kg/day CBD compared to placebo (+5.8%) (P = 0.0017). Liver enzymes increased with both doses of CBD administration.

Conclusions: CBD oil treatment resulted in a significant reduction in total seizures and seizure days compared to placebo when administered orally at dose of 9 mg/kg/day. This supports further studies investigating the role of CBD in the treatment of idiopathic epilepsy in dogs.

¹University of Missouri, Columbia, MO, USA; ²Assistant Professor of Neurology and Neurosurgery, University of Missouri, Columbia, MO, USA; ³Assistant Professor of Veterinary Medicine and Surgery, Neurosciences, University of Missouri, Columbia, MO, USA

Background: Spinal cord injury (SCI) induces global changes in the microRNA (miRNA) expression patterns in the experimental and clinical setting. Identification of dysregulated miRNA could potentially correlate with neurologic outcome and become a prognostic biomarker.

Hypothesis/Objectives: Based upon our miRNA expression profile data, our objective was to validate miRNA biomarker candidates specifically dysregulated in naturally occurring severe SCI in dogs. We hypothesize that relative expression levels of candidate miRNA would correlate with neurologic grade and outcome.

Animals: Serum samples were obtained from a total of 13 dogs (severe: seven paraplegics without pain perception, moderate: three paraplegics with intact pain perception, and three healthy control).

Methods: This is a prospective study. Total miRNA was isolated and transcribed to cDNA. qRT-PCR was carried out against cfa-miR-23a, cfa-miR-574, chr21_19093, cfa-miR-195, cfa-let-7e, chr10_3880_hsa-miR-920 and chrX_46645_mmu-miR-5101. Relative expression levels were calculated by the Delta-Delta Ct method using cfa-miR-16 as a normalization control. T-test were performed and compared in dogs with favorable and unfavorable neurologic outcomes.

Results: Results showed specific up-regulation of cfa-miR-574, chr21_19093 and cfa-miR-195, and down-regulation of cfa-miR-23a, chr10_3880_hsa-miR-920 and chrX_46645_mmu-miR-5101 in dogs without pain perception. cfa-miR-574 demonstrated the most significant (15.9-fold increase, P < 0.04) and consistent up-regulation in the severe group. There was a positive correlation between miRNA expression and neurologic outcome at 6 weeks post-surgery, particularly for cfa-miR-574 in dogs without pain perception (P < 0.02).

Conclusions and Clinical Importance: The results suggest that dysregulated miRNA expression can be used to predict SCI severity and neurologic outcome. A large cohort study is warranted.

¹Purdue University, West Lafayette, IN, USA; ²Assistant Professor, Neurology, Purdue University, West Lafayette, IN, USA; ³Assistant Professor, Neurology, Auburn University, Auburn, AL, USA; ⁴Professor, Neurology, Purdue University; West Lafayette, IN, USA; ⁵Associate Professor, Neurology, Purdue University, West Lafayette, IN, USA

Background: Fibrocartilaginous embolic myelopathy (FCEM) and acute non-compressive nucleus pulposus extrusion (ANNPE) are common causes of canine spinal cord injury with clinical similarities. Limited information is available regarding the prognosis of paraplegic dogs with FCEM and ANNPE.

Hypothesis/Objectives: To describe the clinical features and outcome of paraplegic deep pain positive (DPP) and deep pain negative (DPN) dogs with FCEM and ANNPE.

Animals: Thirty-one client-owned paraplegic dogs with thoracolumbar FCEM or ANNPE presenting to university hospitals between 2012 and 2022.

Methods: Multi-center retrospective study. Paraplegic dogs with a clinical and magnetic resonance imaging diagnosis of FCEM or ANNPE were included. Logistic regression analysis was performed to investigate associations between diagnosis, clinical and imaging variables, and outcome (recovery of independent ambulation or not).

Results: On initial presentation, 14 dogs were paraplegic DPP (8 FCEM, 6 ANNPE), 17 dogs were paraplegic DPN (11 FCEM, 6 ANNPE). Outcome was available for 26 dogs (14 DPP, 12 DPN) with a median follow-up time of 182 days (range, 0–2311). Excluding 2 DPN dogs euthanized at diagnosis, 1/10 DPN dogs (10%) regained independent ambulation, whereas 9/14 DPP dogs (64%) regained independent ambulation. DPN dogs had a significantly higher risk of not regaining independent ambulation compared to DPP dogs (OR: 29.3, CI: 2.1–419.2, P = 0.013). No other variables were associated with outcome (P > 0.05).

Conclusions and Clinical Importance: While the recovery of ambulation is possible, the absence of pain perception appears to be a useful negative prognostic indicator in dogs with severe thoracolumbar FCEM or ANNPE.