Efeito da utilização da metionina protegida da degradação ruminal no desempenho reprodutivo, produtivo e na tolerância ao estresse térmico de vacas nelore

Abstract

Heat stress is a challenge for production systems, due to its effects on metabolism and animal performance, therefore our objective was to evaluate the effects of methionine supplementation protected from ruminal degradation on internal and external temperature, blood concentration of amino acids and on the productive and reproductive performance of beef cows subjected to the reproductive season with high THI. 900 Nelore females were used, distributed evenly into two groups, Control Group (CG; n= 450) and Methionine Group (GM; n= 450). The addition of methionine protected from ruminal degradation (Smartamine® M, Adisseo, Antony, France) occurred at a proportion of 3g for every 100g of mineral supplement. Internal (IT) and external (TE) temperatures were evaluated between days -9 and -2, in relation to the day of artificial insemination. Blood samples were collected through puncture of the coccygeal vein, on days -28, -9, 14 and 28, to evaluate plasma amino acids, HSP and progesterone. Weight gain of cows and calves and body condition score (BCS) were evaluated. Reproductive variables were evaluated by ultrasound and pregnancy diagnosis was made 31±2 and 60±2 days after TAI. The fixed effects of treatment (methionine and control), birth order (primiparous and multiparous) and their interactions were considered. Temperature, metabolism and performance data were evaluated by repeated measurements. Binary data (pregnancy rate at 30 and 60 days) were compared using the chi-square test. The average THI ranged between 67 and 78. There was no effect of methionine supplementation on internal temperature (GC=38.92±0.036 and GM=38.93±0.036; P=0.82), on external temperature (GC= 32 .80±0.42 and GM=33.19±0.45; P=0.53) and pregnancy rate (GC= 65% and GM=65.4; P=0.92). For the average daily gain (ADG) of cows, we found a positive effect of methionine supplementation (GC= -0.246±0.02; GM=0.140±0.02, P<0.001). For the calves' performance, the methionine group was superior compared to the control animals (GC=0.837±0.008 and GM=0.884±0.008; P<0.001). In the metabolic profile, supplementation with methionine improved the balance of plasma amino acids and the relative expression of HSP 70 (p<0.05). Therefore, it is concluded that supplementation with methionine, protected from ruminal degradation, improves the weight gain of cows and calves, the concentration of plasma amino acids and the gene expression of HSP70. However, it had no effect on body temperature and reproductive performance.