Effects of rumen-protected leucine on production performance and starch digestion in the small intestine of lactating goats

This study was conducted to evaluate the effects of rumen-protected leucine (RP-Leu) on production performance and starch digestion in the small intestine of lactating goats. Thirty lactating goats (body weight: 43.07 ± 5.06 kg; first parity, day in milk: 135 ± 15 days; milk yield: 2.06 ± 0.44 kg/d) were randomly assigned into one of the following dietary treatments: (1) CON: basal diet and (2) RPL: basal diet + 10.6 g/d RP-Leu. The experiment lasted 65 days, 15 days for adaption, 45 days for treatment, and 5 days for measurement. Goats fed the diet supplemented with RP-Leu had higher (P < 0.05) average daily gain than those fed the CON diet, but no significant difference (P > 0.05) was observed in milk yield and milk composition. The addition of RP-Leu did not affect dry matter intake, apparent total tract digestibility of starch, and rumen fermentation parameters in lactating goats (P > 0.05). The feces of goats fed the diet supplemented with RP-Leu had reduced molar proportion of butyrate and increased pH and molar proportion of acetate compared with that of goats fed the basal diet (P < 0.05). Dietary supplementation of RP-Leu increased the relative abundance of Christensenellaceae, Christensenellaceae_R-7, Ruminococcaceae, and Ruminococcus in feces, while reducing the relative abundance of Lachnospiraceae and Anaerostipes (P < 0.05). Serum low-density lipoprotein and free leucine were greater (P < 0.05) for goats fed the RPL diet than those of goats fed the CON diet. In addition, the concentrations of total cholesterol and high-density lipoprotein in goats fed the RPL diet tended to be higher (0.05 ≤ P < 0.10) than those of goats fed the CON diet. In conclusion, dietary supplementation of RP-Leu probably improved starch digestibility in the small intestine of lactating goats showing as reduced hindgut starch fermentation and unchanged starch intake, apparent total tract digestibility of starch and rumen fermentation parameters.