PSVI-1 - Effects of Rumen-protected Methionine on Reproduction and Body Temperature of Nelore Cows in Hot and Humid Environments

Abstract: This study aimed to evaluate the effects of dietary supplementation of rumen-protected methionine (RPM) on the body temperature and conception rate of Nelore cows exposed to high temperature and humidity index (THI) values. This study was realized on a commercial beef farm located in the north of Brazil (5º 31’ 39” S, 48º 49’ 18” W). At d-31, 31 days before the FTAI protocol, a total of 563 lactating multiparous Nelore cows were divided into two treatments, with three blocks each, the control group (CG) and methionine group (MG). Both groups were kept on tropical pastures and received a mineral supplement. The MG Group was supplemented with 3g RPM/100g during 77 days, and the expected mineral supplement intake of both groups was 100g/cow/day. Between d0 and d9 of the FTAI protocol, a subset of groups of cows (n=142) remained with a data logger attached to the progesterone device, to monitor intravaginal temperature (IT) every 30 min. During the period that the cows remained with the dataloggers the minimum, average, and maximum THI were 72.76, 78.02, and 83.28, respectively. Pregnancy diagnosis was realized 35 days after the artificial insemination and the conception rate was calculated as the number of pregnant cows/inseminated cows. Data were analyzed using the JMP GLIMMIX procedure. RPM supplementation did not affect the conception rate (CG = 64.36% vs. MG = 58.19%, P >0.05). Intravaginal temperature from day 1 to day 8, between 0630 and 2030 h and between 2200 and 0100 h were lower (P≤0.05) for MG in comparisonwith CG. The average and the maximum IT were, respectively, 38.94ºC, 40.88ºC for MG and 39.02ºC, and 41.38ºC for CG. In conclusion, the supplementation of rumen-protected methionine reduced the internal body temperature in Nelore cows submitted to high THI environments, during the hottest hours of the day, but does not affect the conception rate.