Rumen-protected methionine modulates body temperature and reduces the incidence of heat stress temperatures during the hottest hours of the day of grazing heat-stressed Bos indicus beef cows

1 INTRODUCTION

The global temperature has continuously increased in recent decades. In 2019, the global average temperature was 1.1°C higher than during the pre-industrial period, marking it as the second warmest year on record (World Meteorological Organization [WMO], 2019). Livestock directly experiences heat stress (HS) as environmental temperatures (ETs) increase beyond the thermoregulation threshold (Hansen, 2004). Feed intake, milk yield, meat quality, physiological functions, and reproductive performance of cattle have negative impacts because of HS (Guo et al., 2018; Lees et al., 2019; López-Gatius & Hunter, 2020; Rahman et al., 2018; Zhang et al., 2020).

Over the last few decades, parameters used to measure HS in the environment and animals include the temperature–humidity index (THI), respiratory and heart rate monitoring, and internal body temperature (Dikmen & Hansen, 2009; Ji et al., 2020; Kaufman et al., 2018). These tools aid producers in deciding the strategic timing and actions to mitigate HS, such as management and nutritional strategies. Providing shaded areas for cattle grazing on pastures or in feedlots (Grandin, 2016; Van Laer et al., 2014), as well as dietary supplementation of vitamin E, methionine, and betaine, have been applied to alleviate HS effects, leading to improved cattle production and reproductive performance (Negrón-Pérez et al., 2019; Zhang et al., 2020).

The metabolism of animals shifts due to HS. Instead of utilizing lipolytic pathways as a source of glucose, heat-stressed cows increase skeletal-muscle protein catabolism, where amino acids play an important role (Baumgard & Rhoads, 2013). Methionine, an essential amino acid, must be supplied in the diet (Parkhitko et al., 2019). Studies on rats subjected to dietary methionine restriction have shown increased body temperature, cell respiration rate, and expression of uncoupling protein 1 (UCP1) compared with rats without dietary methionine restriction (Hasek et al., 2010; Patil et al., 2015). Moreover, methionine supplementation improves protein synthesis, prevents proteolysis (Del Vesco et al., 2015), and participates in the process of heat sensitivity (Fricke et al., 2019).

Methionine supplementation for cattle should be in the rumen-protected form to avoid rumen degradation and increase small intestine supply (Sudekum et al., 2004). In beef heifers, rumen-protected methionine (RPM) lowered internal body temperature, increased body weight gain (BW), and increased follicle size in Brangus (Dominguez et al., 2020), and reduced stress during transportation (Alfaro et al., 2020). Supplementation of beef cows with methionine hydroxy analog also altered maternal plasma concentration of glucose (Palmer et al., 2020) and offspring muscle gene expression (Liu et al., 2020). Despite the better thermoregulation of Bos indicus vs. Bos taurus breeds (Hansen, 2004), the benefits of methionine supplementation observed in other species and cattle categories make this supplementation strategy a suitable alternative to mitigate HS in B. indicus beef cows.

We hypothesized that RPM supplementation will reduce internal body temperature of Nelore cows during HS and improve their reproductive performance in hot and humid environments. Hence, our objectives were to evaluate the effects of RPM supplementation on body thermoregulation and conception rate of Nelore cows exposed to high THI.

2 MATERIAL AND METHODS

The experiment was conducted on a commercial beef farm in São Domingos do Araguaia, PA, Brazil (5° 31′ 39″ S, 48° 49′ 18″ W), from November 2019 to March 2020. All animals were cared according to experimental protocols approved by Animal Experimentation Ethics Committee of the Federal University of Pelotas, under protocol number 5069.

3 RESULTS

Effects of treatment were not detected (P > 0.23) for supplement intake, forage allowance, forage mass, and treetop area (Table 1). Total rainfall during the FTAI protocol was 34, 84, and 134 mm for blocks 1, 2, and 3, respectively.

Effects of treatment × hour of the day were detected (P < 0.0001) for IT. From 1330 to 1730 h and 1830 to 1900 h, IT was greater (P < 0.05) for CG versus MG cows (Figure 1). Effects of treatment × hour of the day were detected (P < 0.0001) for the percentage of IT above 39.3°C (Figure 2). From 1330 to 1830 h, the MG had a lower percentage of temperature reads >39.3°C, with the greatest difference at 1600, where the CG had 58.96% of the temperatures >39.3°C, and the MG had 28.51%. At 1300 and 1900 h, the MG tended to have a lower percentage of IT >39.3°C (P ≤ 0.09).

Effects of treatment, THI level, and treatment × THI level were detected (P ≤ 0.0001) for IT (Table 3). In the low THI level (72 ≤ THI < 76), no effects of RPM supplementation were detected (P = 0.26). In the moderate and high THI levels, the MG had lower IT than CG (P ≤ 0.02). The greater IT difference was observed in the high THI level (CG = 39.34°C, MG = 39.16°C). Effects of treatment were not detected (P = 0.17) for conception rates, which were 58.2% and 64.4% for MG and CG cows, respectively (Table 3).

4 DISCUSSION

In the current study, forage mass, forage allowance, and daily supplement intake data did not differ between treatments. Forage allowance was above the minimum threshold to limit forage DM intake (Inyang et al., 2010). Supplement intake results showed that the intake of 3 g of Smartamine®/head/day was successfully achieved for MG cows. Previous studies utilized RPM supplementation for beef cattle at different doses of absorbable methionine, ranging from 2.4 to 4.9 g/day (Alfaro et al., 2020; Dominguez et al., 2020; Silva et al., 2021). It is important to note that different research conditions among these studies, such as animal categories and management practices (e.g., grass vs. hay), may result in different animal methionine requirements (Cantalapiedra-Hijar et al., 2020). In our study, however, animal category and management practices were not a concern since all the animals were from the same category, and cows from each block were rotated in the same pastures.

The efficiency of maintaining constant body temperature in cattle is influenced by ET and humidity changes. Cattle lose body heat primarily by evaporation, but this mechanism is not effective in high-THI environments, leading to increased heat load and HS (Almeida et al., 2020). Daily cumulative heat load observed herein indicated that all cows experienced HS as it was consistently >34. When daily cumulative heat load is >34, cattle capacity to maintain internal temperature <39°C is jeopardized, regardless of breed (Mateescu et al., 2020). The severity of the effects of HS depends on the duration and intensity to which the animals are exposed to high THI. The THI values observed herein indicated that cows were under moderate to high HS (Cordeiro et al., 2020; Mateescu et al., 2020). Mader et al. (2010) observed that the thermoregulation capacity of animals is related to their cooling ability at night, highlighting the importance of evaluating the daily cumulative heat load rather than just the THI peak. Despite this, in our study, it seems that the cows exposed to moderate or high HS, the internal temperature differences were not maintained at night, indicating that the CG could return to normal internal temperature during the night. This observation may partially explain the lack of differences in reproductive variables between the groups.

Studies demonstrated that the pregnancy rate is reduced when Nelore cows are exposed to THI > 75.7 (Cordeiro et al., 2020) and when B. taurus beef cows are maintained in environments with THI > 73 (Amundson et al., 2006). Our study observed average THI values greater than these studies that evaluated the THI effects on pregnancy rate, with the maximum THI observed, in our study, greater than 82 in all three blocks. We expected pregnancy rate improvement with RPM supplementation because previous studies from our group showed that Brangus heifers supplemented with RPM had larger follicles than those not supplemented (Dominguez et al., 2020). Also, Toledo et al. (2017) observed that feeding RPM increased embryo diameter and volume in multiparous Holstein cows. Despite the higher IT for CG, the values observed for these animals may not be enough to negatively impact pregnancy rates. Other factors that may explain the lack of pregnancy rate differences between treatments was the high number of cows with low BCS on d0 of the FTAI protocol, in which more than 35% of the cows had BCS ≤ 2.5. Pfeifer et al. (2017) mentioned that cows with moderate to good BCS (2.75 ≤ BCS ≤ 4.25) tend to be more fertile than those outside this interval. In addition, D'Occhio et al. (2019) verified that, compared with cows with 3.0–3.5 BCS, those with 2.0–2.5 BCS have lower insulin and glucose blood levels, which directly impact cow reproduction.

The 30-min average IT demonstrates the dynamics of the body temperature during the day, and if it exceeds or does not reach the physiological threshold, while evaluating the percentage of IT above this threshold (39.3°C; Du Preez, 2000) indicates that more animals had HS readings during the hottest hours of the day. From 14:00 to 18:30 h, CG had at least 16% more readings above physiological parameters than MG (Figure 2). The percentage of cows with IT above 39.3°C (Table 3) was calculated based on the animals that had at least one reading on this range each day. The differences observed in the daily percentage of animals and the hourly percentage of IT above 39.3°C is a consequence that animals in the same group may increase or decrease their body temperature earlier or later than the others due to different mechanisms to regulate body temperature, such as individual behavior, metabolism or environment (Gaughan et al., 2010.; Slimen et al., 2015). In the current study, these two measurements allowed to understand that MG cows had a reduction in hours of the day and animals exposed to not physiological IT, compared with CG.

When a group has lower IT in moderate and high THI but not in low THI, it demonstrates that this group has different mechanisms to control body temperature than the other. In the present study, MG cows had lower IT in moderate and high THI compared with CG, with the average IT not exceeding the physiological threshold in any category (Mateescu et al., 2020), while in the CG group the average IT exceeded it when exposed to high THI. These outcomes demonstrate that RPM effectively played an important role on thermoregulation during the hottest hours of the day. The mechanism that the methionine helps thermoregulation still need to be elucidated, however, it is possible that the amino acids play a crucial role in the angiogenesis process (Oberkersch & Santoro, 2019), and the supplementation with methionine was able to help maintain homeostasis in heat stressed chickens (Lee et al., 2021), making the vasodilatation likely a mechanism for methionine to help the thermoregulation process.

B. indicus animals are more resistant to hot and humid environments due to a series of adaptations that occurred during the evolution from B. taurus. Cellular resistance to elevated temperatures and physiological and phenotype changes are some of the features that B. indicus cattle acquired to improve thermotolerance (Hansen, 2004; Mateescu et al., 2020). Despite this better adaptability, MG cows had reduced IT compared with CG cows. This reduction was previously determined by Dominguez et al. (2020) in Brangus heifers fed 4-g RPM. This reduction in IT may be explained by methionine regulation of thermogenin (UCP-1), which was found in a study in broiler (Del Vesco et al., 2014). UCP-1 is a thermogenic protein whose expression increased in rats fed a methionine-restricted diet. Also, the rats showed higher body temperatures than those not submitted to methionine restriction (Hasek et al., 2010). Heat-stressed animals have an increase in oxidative stress by increasing the amount of reactive oxygen species and reducing the number of antioxidant enzymes (Abdelnour et al., 2019; Slimen et al., 2015). Alfaro et al. (2020) found that RPM pretransportation could reduce the transport stress of beef cattle by reducing oxidative stress. Also, the supplementation of methionine on another species found the same increase in antioxidant response by the methionine supplementation (Del Vesco et al., 2015).

Shade is an important tool to mitigate HS effects and different shade types affect cattle internal body temperature (Oliveira et al., 2019). Shade influences physiological parameters, such as body core temperature and respiration rate of animals exposed to THI values ≥78 (Brown-Brandl et al., 2005). Although treetop area was not statistically different among paddocks, it was numerically larger in CG on blocks 1 and 2, and MG on block 3 compared with MG on blocks 1 and 2, and CG on block 3, respectively, which may have reduced the heat challenge on those cows. Despite that, the measured treetop area was bigger than the minimum recommended for grazing cattle in all the paddocks. Armstrong (1994) determined that at least 5.6 m²/cow for animals reared in hot and wet environments, while Van Laer et al. (2014) recommended 3.28 m² of lying space in the shade for 700 kg beef cows. Also, the use of shade is more effective in mitigating HS in environments with high temperature and low humidity than when both temperature and humidity are high (Renaudeau et al., 2011), such as the conditions of our experiment.

In conclusion, 3 g of RPM supplementation effectively lowered internal body temperature and possibly altered the critical THI threshold in heat-stressed Nelore cows. Therefore, RPM effectively modulated body thermoregulation, even though its impact on reproductive outcomes in hot and humid environments appears limited.

CONFLICT OF INTEREST STATEMENT

The authors declare no conflict of Interests for this article.