Sweat osmolarity shows intra-animal regional variation in the horse
Abstract
enBackground
Sweating is important in regulating body temperature but can be a source of loss of both fluids and electrolytes. Although the process has been studied in horses, the variation in sweat osmolarity across the body has not.
Objectives
This work describes an investigation to determine if there is regional variation in the osmolarity of sweat across different anatomical regions of the horse.
Animals
Ten horses were used in the study and were animals either stabled for riding lessons or had livery on-site.
Methods
Sweat samples were collected from five regions on each horse following exercise and the osmolarity measurements were made using an Osmomat 030 (Gonotec, Berlin, Germany). Values were analysed by paired t-tests and analysis of variance.
Results
Samples from the back and ears had statistically (P < 0.05) lower osmolarity values than those seen for the neck and forelimb, with thigh values intermediate between the other two sets of values.
Conclusions and clinical importance
Previous studies have used osmolarity values based on the sweat collected from the horse's back. The current work demonstrates that these values are probably an underestimation of electrolyte loss, which may have implications for the composition and administration of rehydration compounds.
Résumé
frContexte
La sudation est importante pour la régulation de la température corporelle mais peut également être une source de perte de fluides et d’électrolytes corporels. Bien que le processus ait été étudié chez le cheval, la variation de l'osmolarité de la sueur à travers la peau ne l'a pas été.
Objectifs
Cette étude décrit la variation régionale de l'osmolarité de la sueur sur différentes régionscorporelles du cheval.
Sujets
Dix chevaux ont été inclus dans cette étude et étaient des chevaux de club ou de pension.
Méthodes
Des échantillons de sueur ont été prélevés sur cinq régions de chaque cheval à la suite d'un exercice et des mesures d'osmolarité ont été réalisées à l'aide d'Osmomat 030 (Gonotec, Berlin, Germany). Les valeurs ont été analysées par des tests-t par paire et des analyses de variance.
Résultats
Les échantillons du dos et des oreilles étaient statistiquement (P < 0.05) de plus faible osmolarité que ceux du cou et des membres antérieurs avec des valeurs intermédiaires étroites entre les deux autres valeurs de lots.
Conclusions et importance clinique
Les étudesprécédentes ont étudiées l'osmolarité sur des valeurs basées sur la sueur prélevée sur le dos des chevaux. Cette étude démontre que ces valeurs sont probablement une sous estimation des pertes d’électrolyte, ce qui peut avoir des implications pour la composition et l'administration des composes de réhydratation.
Resumen
esIntroducción
la sudoración es importante para regular la temperatura corporal pero puede ser una fuente de pérdida de fluidos y electrolitos. Aunque el proceso ha sido estudiado en caballos, no se ha estudiado la variación en la osmolaridad del sudor en diferentes partes del cuerpo.
Objetivos
este trabajo describe una investigación para determinar si hay variaciones regionales en la osmolaridad del sudor en diferentes regiones anatómicas del caballo.
Animales
se utilizaron 10 caballos en el estudio que eran animales o bien estabulados para lecciones de monta o bien libres en el recinto.
Métodos
se tomaron muestras de suduración de cinco regiones de cada caballo tras el ejercicio y los valores de osmolaridad se determinaron utilizando un Osmomat 030 (Gonotec, Berlín, Alemania). Los valores se analizaron mediante pruebas de t pareadas y análisis de varianza.
Resultados
las muestras de la espalda y los oídos fueron estadísticamente (P < 0,05) menores en su osmolaridad que los valores de osmolaridad del cuello y extremidades anteriores, con los valores de los muslos siendo intermedios entre estos dos extremos de valores.
Conclusiones e importancia clínica
estudios previos han utilizado los valores de osmolaridad basados en sudor recogido de la espalda del caballo. Este trabajo demuestra que estos valores son probablemente una estimación a lo bajo de la pérdida de electrolitos, lo cual puede tener implicaciones en la composición y administración de los compuestos rehidratantes.
Zusammenfassung
deHintergrund
Schwitzen ist wichtig bei der Regulierung der Körpertemperatur, kann aber auch die Quelle von sowohl Flüssigkeits- wie auch Elektrolytverlust sein. Obwohl der Prozess bei den Pferden untersucht worden ist, gibt es keine Daten über die Verteilung der Osmolarität des Schweisses über den ganzen Körper.
Ziele
Diese Arbeit beschreibt eine Untersuchung, um eine eventuelle regionale Variation der Osmolarität des Schweisses in verschiedenen anatomischen Körperregionen des Pferdes zu bestimmen.
Tiere
Zehn Pferde wurden in dieser Studie verwendet, es handelte sich um Tiere, die entweder für den Reitunterricht aufgestallt waren oder als Pensionspferde eingestellt waren.
Methoden
Es wurden nach der Bewegung Schweißproben aus fünf verschiedenen Körperregionen eines jeden Pferdes gesammelt und die Osmolaritätsmessungen mittels Osmomat 030 (Gonotec, Berlin, Deutschland) durchgeführt. Die Ergebnisse wurden mittels gepaartem t-Test und Varianzanalyse ausgewertet.
Ergebnisse
Die Proben vom Rücken und von den Ohren wiesen statistisch (P<0,05) eine niedrigere Osmolarität auf als jene des Halses und der Vorderextremitäten, die Werte der Oberschenkel lagen wiederum genau zwischen den Werten dieser beiden Gruppen.
Schlussfolgerungen und klinische Bedeutung
Frühere Studien haben die Osmolaritätswerte, die von Schweiß, der vom Rücken des Pferdes gesammelt wurde, verwendet. Die vorliegende Studie zeigt, dass diese Werte möglicherweise den Elektrolytverlust unterschätzen, was wiederum Implikationen für die Zusammensetzung und die Verabreichung von Rehydrierungskomponenten haben könnte.
Abstract
ja
Abstract
zh
Introduction
Production of sweat is an important process in mammals because it allows for an evaporative cooling process which assists in regulation of body temperature, either at times of high ambient temperature or during exercise when there is an increase in metabolic processes occurring in the body.1 Horses have two different types of sweat glands: apocrine and merocrine, with the majority being apocrine.2 In general, merocrine glands are thought to be restricted to the hairless areas (e.g. the frog), whilst apocrine sweat glands are distributed across the entire body,2 meaning that all sweat seen on a horse can be regarded as being of apocrine origin. Because the apocrine sweat glands open into hair follicles and in the horse there is one hair follicle per root hair, this means that hair follicle number is a representation of the number of apocrine sweat glands.
Based on this relationship between hair follicles and sweat glands, work was performed to estimate the density of sweat glands at different parts of the body at 46 loci across seven sites on the horse's body.2 Values varied greatly across the body, from around 500 hairs cm−2 in the pubic region to over 1100 hairs cm−2 in lateral areas of the distal pelvic and thoracic limbs. Thus it is already clear that the distribution of sweat glands across the horse is not uniform.
Sweat is composed of a number of different chemicals, including ions (e.g. Cl−, Na+, K+) and proteins (e.g. latherin). However, many previous reports have employed generic osmolarity investigations, rather than looking at specific components of the sweat. Previous studies have been published on sweat composition in horses, including examples of osmolarity values. One such study found that the range was typically 290–320 mOsm/L.3 There have also been differences detected in the osmolarity of sweat depending on environmental conditions, for example 303 mOsm/L in cool dry conditions compared with 339 mOsm/L in hot dry conditions,4 and 535–565 mOsm/L following adrenaline infusion.5
Regional sweat composition, in terms of osmolarity, has been shown to vary in humans.6 To the best of the authors' knowledge, no such investigation has been undertaken in the horse. This work describes an investigation into regional variation in the osmolarity of sweat across different regions of the horse's body.
Materials and methods
Collection and storage of sweat
Collections were carried out in Ceredigion, Wales, and Florida, USA. Animals ranged from 2 to 17 years of age (mean = 9.6; SE = 3.04). Both mares and geldings were used for sampling; animals included a range of different breeds (quarter horse, Irish draft cross, British warmblood, Welsh section D ponies, Irish sport horse and thoroughbred cross). All animals were sound at the time of sampling and samples were collected with the consent of the owners.
In a pilot study to investigate recovery of sweat, paper towels were shown to give a greater recovery than a number of commercially available swabs. Using this approach it was possible to replicate the pattern of differences in osmolarity at different parts of the human body, as previously reported,6 as well as successfully collect samples from horses.
The regions of the horse which were to be used for sample collection (medial aspect of foreleg, thoracic/lumbar interphase of the back, ear, jugular region of the neck and inner thigh) were washed before horses were exercised for 20–30 min. Immediately after exercising, sweat samples were collected from ten horses; gloves were worn throughout collections to minimise the risk of contamination from human sweat. Collection of sweat was performed with paper towels at the five regions on the horse listed above. Immediately after collection samples were placed in individual plastic containers before being chilled at 4°C where samples were to be studied imminently, or frozen and stored in a freezer at −20°C where samples were not going to be used shortly after collection. Samples were maintained at this temperature until used (for a maximum of 2 weeks).
Measurement of osmolarity of sweat
Immediately prior to analysis samples were raised to ambient temperature and were centrifuged twice at 1000 g for 3 min. From the liquid recovered post-centrifugation 50 μL of sweat was used for analysis from each sample. Osmolarity measurements were made using a freezing point depression osmometer (Osmomat 030; Gonotec, Berlin, Germany). This machine was calibrated using 0.300 and 0.850 Osmol/kg standards and working on the principle that deionised water freezes at 0°C and a solution of 1 Osmol/kg freezes at −1.858°C.
Statistical analysis
Sweat osmolality values from each study region were compared for kurtosis and skewness to determine whether data were normally distributed. Six samples posed problems due to crystallization and these samples were removed from analysis. In all cases there were samples from at least eight horses per body location and in all cases each horse provided samples from at least four body locations. Data were analysed by paired t-tests to check for differences between anatomical regions. In addition, F-test supported t-tests were performed for inter-horse variation. Analysis of variance (ANOVA) was also performed following compensation for missing data values as previously described.7
Results
There were significant differences in the osmolarity values of sweat collected from different regions of the study horses (see Table 1). Differences were also detected following ANOVA calculations (P < 0.05). The higher osmolarity values did not coincide with those regions which have the highest density of hair follicles. Likewise, based on published skin thickness values,8 there was no apparent relationship between the thickness of the skin and the osmolarity values.
| Region | Number of samples | Mean osmolarity value | SEM |
|---|---|---|---|
| Forelimb | 10 | 1.321 a | 0.153 |
| Back | 10 | 0.842 b | 0.092 |
| Ear | 8 | 0.882 b | 0.082 |
| Neck | 8 | 1.533 a | 0.229 |
| Thigh | 8 | 0.969 a, b | 0.190 |
Discussion
All of the values in Table 1 are higher than previously reported figures,3, 4 although it is worth noting that the highest figure cited previously was as a result of adrenaline infusion prior to collection.5 In the current work the horses had just completed exercise and so their adrenaline levels may have been elevated, giving a value higher than that seen in previous publications. In addition, previous work concentrated on sweat samples collected from regions such as the back, which the current study suggests is one of the regions with the lowest osmolarity value. Given the disparity in sweat production across different regions of the body, it can be suggested that the most common site for sweat collection in previous work may not have given a true reflection of the possible electrolyte balance. This, in turn, may mean that estimated loss of electrolytes may have been underestimated previously.
In conclusion, the data presented here identify that there is variation in the osmolarity between different anatomical regions in the horse and, by inference, this means that there are regional differences in the composition of the sweat.
