PSXIV-3 Reproductive performance of Bos indicus cows supplemented with a low dose of rumen-protected methionine.

Abstract Previous studies from this research group on beef cows supplemented with rumen-protected methionine (RPM) at 2.5 and 3.6 g of metabolizable methionine showed a positive effect on reproductive parameters. This study evaluated ovarian function and pregnancy per artificial insemination (P/AI) in Nelore (Bos indicus) cows supplemented with a low dose of rumen-protected methionine (RPM). The experiment was conducted at Fazenda Figueira, located in southern Brazil (23º 34’ 26” S, 50º 58’ 14” W), during the summer breeding season. On day -28, 28 days before a timed-AI (TAI) protocol, a total of 1,093 primiparous and multiparous cows, with 25 ± 19 days postpartum were divided into two treatments with six blocks each: Control Group (Con, n = 548) and Methionine Group (Met, n = 546). Both groups were kept on tropical pasture and received a mineral supplement ad libitum. The Met group was supplemented with 1.8 g of RPM per 100 g of mineral supplement (Smartamine® M, Adisseo, Antony, France) for 60 days (from d-28 until 32 days after TAI), with an expected mineral supplement intake of 100 g/cow/day in both groups. Pregnancy diagnosis was performed 32 days after AI using transrectal ultrasound. Follicle diameter and follicular growth rate were evaluated on days -2 and 0 (n = 313), whereas corpus luteum (CL) volume (n = 138) and plasma progesterone (P4) concentration were evaluated on day 14 (n = 138). Data were analyzed using the GLIMMIX procedure in SAS software (SAS Institute Inc., Cary, NC, USA, version 9.4), considering treatment, block, and their interaction as fixed effects, while pasture and cows were included as random variables. No interaction effects between group and block were detected (P > 0.05). No significant effects were detected for P/AI, follicle diameter on d-2 and d0, or CL volume (P > 0.05). Circulating P4 was lower (P = 0.02) for Met vs. Con cows. A tendency was detected (P = 0.08) for increased follicular growth rate on Met cows. Therefore, a dose higher than 2.5g of metabolizable methionine should be used in order to have the expected positive reproductive response in beef cows. We sincerely thank Adisseo for their financial support in this study. Their contribution was essential for the development and execution of this research.