Rumen-Protected Leucine Improved Growth Performance of Fattening Sheep by Changing Rumen Fermentation Patterns

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 norank_f_F082 and norank_f_UCG-011 (p < 0.05). Phenylalanine, isoleucine, valine, and leucine were negatively correlated with norank_o_Bacteroidales (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.