Wuwei Jianpi San Improves Growth Performance and Immune Status in Yaks Through Modulation of Rumen Microbiota and Host Metabolism

To investigate the effects of Wuwei Jianpi San (WJPS), a Chinese herbal compound feed additive, on rumen microecology, host metabolism, and immune function in healthy yaks (Bos grunniens), and to determine the optimal supplementation level, 32 yaks with similar initial body weight were randomly assigned to four groups: a control group and three groups receiving 0.5%, 1.0%, or 2.0% WJPS for 90 days. Growth performance, hematological indices, serum antioxidant and immune parameters, tryptophan metabolites, ruminal short-chain fatty acids (SCFAs), and rumen microbiota were analyzed. WJPS supplementation improved growth performance, as shown by a reduced feed-to-gain ratio in all treated groups and tended to increase average daily gain in the 2.0% group. It also enhanced hematological, antioxidant, and immune status, evidenced by increased white blood cell (WBC) and lymphocyte (Lym) counts and elevated interleukin-2 (IL-2), immunoglobulin G (IgG), and superoxide dismutase (SOD) levels. Moreover, 2.0% WJPS increased total SCFAs, acetate, and n-butyrate, while WJPS reduced kynurenine pathway metabolites, including kynurenine, 3-hydroxykynurenine, and quinolinic acid. Metagenomic analysis showed that WJPS tended to shape rumen microbial composition by increasing Bacillota and decreasing Bacteroidota, and these microbial changes were associated with host immune indices and tryptophan metabolism. Overall, 2.0% WJPS showed the best comprehensive effect.