This experiment investigated the effects of rumen-protected leucine (RP-Leu) supplementation on growth performance, rumen fermentation parameters, and rumen microbiota of fattening sheep. Forty fattening sheep (19. 03 ± 0. 38 kg) were randomly divided into four groups. The four groups were fed the basal diet supplemented with RP-Leu at 0 (L-0), 0. 5 (L-0. 5), 1. 0 (L-1. 0), or 1. 5 (L-1. 5) g/d. The experimental period lasted 67 d. The results demonstrated that compared with the L-0 group, the L-1. 0 and L-1. 5 groups significantly increased the average daily gain (ADG) by 22. 2% and 18. 0%, respectively (p < 0. 05), and reduced the feed-to-gain ratio (F: G ratio) by 20. 0% and 13. 4% (p < 0. 05) ; the L-1. 5 group significantly increased the concentrations of propionate and isovalerate (p < 0. 05) and significantly decreased the acetate to propionate ratio (A: P) by 25. 7% (p < 0. 05) ; and the L-1. 0 group significantly decreased the concentrations of free branched-chain amino acids (BCAAs) in rumen (p < 0. 05). A microbiota analysis showed that RP-Leu enriched the abundance of fiber-degrading bacteria. A correlation analysis showed that acetic acid and A: P were positively correlated with norankfF082 and norankfUCG-011 (p < 0. 05). Phenylalanine, isoleucine, valine, and leucine were negatively correlated with norankₒBacteroidales (p < 0. 05). In conclusion, RP-Leu improved the growth performance of fattening sheep by changing the rumen fermentation parameters and patterns; the optimal supplementation level is 1. 0 g/d.
Li et al. (2025) studied this question.