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

Abstract

AbstractThis study evaluated the effects of supplementation of rumen‐protected methionine (RPM) on body thermoregulation and conception rate of Nelore cows exposed to high temperature–humidity index (THI). On −31 days before the artificial insemination protocol, 562 lactating, multiparous cows were assigned to receive (MG) or not (CG) RPM supplementation (3 g/cow mixed into 100 g of mineral supplement). Both groups remained in tropical pastures and received supplementation for 77 days. A subset of cows (n = 142) remained with an intravaginal thermometer collecting intravaginal temperature (IT). The respective minimum, average, and maximum environmental THI were 72.8, 78.0, and 83.3. 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 higher (P < 0.05) for CG versus MG cows when exposed to moderate and high THI. The supplementation with RPM did not affect conception rate (CG = 64.4% vs. MG = 58.2%; P > 0.05). In conclusion, 3 g of RPM supplementation lowered internal body temperature and possibly altered critical THI threshold in Nelore cows with no impact on reproduction.