Effect of Supplemental Bamboo Leaf Extract on Milk Production, Composition, Biochemical Indices, and Fecal Microbiota Diversity in Grazing Yili Mares

<b>Purpose</b>: This study investigated the effects of dietary bamboo leaf extract (BLE) on milk parameters and intestinal microbiota in lactating <i>Yili</i> mares. <b>Methods</b>: Twenty-four <i>Yili</i> mares of similar age (10 ± 2 years), weight (360.62 ± 15.23 kg) and body condition were selected for this study and randomly divided into four groups of six mares each: an untreated control group (CG) and three experimental groups (EG1, EG2, EG3) were fed a basal diet supplemented with 0, 10, 20, or 30 g/day of BLE, respectively, for 60 days. Then, horse milk composition, antioxidant activity, and immunoglobulin levels along with the relative abundance of fecal microbiota were measured. <b>Results</b>: Compared with the control group, supplementation with BLE for 60 days significantly improved milk yield and composition. The protein content in the EG1 was significantly higher than that in the CG, the milk yield and fat content in the EG2 was significantly higher than that in the CG, and the lactose content in the EG3 was significantly higher than that in the CG. BLE also significantly increased the milk's antioxidant capacity, vitamin C, IgG, IgM, and IgA levels, with the antioxidant and immune properties in the EG2 being significantly higher than those in the CG. Furthermore, BLE feeding promoted communities of beneficial intestinal microbes. Bacteria associated with energy metabolism and organic matter decomposition increased significantly in BLE-fed groups, especially the EG2, which had elevated abundance of <i>UCG-002</i> and the <i>NK4A214_group</i>. BLE also significantly reduced the abundance of Euryarchaeota, Verrucomicrobiota, <i>Methanobacteriaceae</i>, and <i>Methanobrevibacter</i>. <b>Conclusions</b>: Dietary supplementation with bamboo leaf extract is a safe and inexpensive way to enhance milk yield and quality and to promote the growth of beneficial intestinal microbes in <i>Yili</i> horses.