Yeast Culture Alleviates High-Concentrate Diet-Induced Rumen Fermentation Disturbances and Modulates the Rumen Microbiota and Metabolome in Lambs.

This study evaluated whether yeast culture (YC) supplementation could alleviate rumen disturbances induced by a high-concentrate diet in lambs. Forty-five three-month-old Du × Han F1 male lambs were assigned to control (CON), high-concentrate (HC), or HC supplemented with 0.5% YC groups (n = 15 each) for 60 days; six lambs per group were sampled for serum biochemistry, rumen fermentation, 16S rRNA gene sequencing, and untargeted metabolomics. Compared with CON, HC markedly reduced rumen pH (6.55 vs. 5.52) and the acetate-to-propionate ratio (2.67 vs. 1.31), whereas YC increased these values to 6.32 and 2.35, respectively (p < 0.05). YC also increased acetate and butyrate concentrations and reduced propionate relative to HC, while serum ALT returned to a level comparable to CON. YC partially reversed these fermentation changes and restored serum ALT to CON-comparable levels. YC also increased the Shannon index relative to HC and showed features relative to CON. LEfSe identified g__Mitsuokella, g__Megasphaera_A_38685, g__Succiniclasticum, g__Parafannyhessea, and g__CAG-269 as candidate YC-responsive genera. Metabolomics identified 188 and 436 differential metabolites in CON versus HC and HC versus YC, respectively, mainly involving amino acid and cofactor metabolism. Several metabolites shifted toward CON levels, and correlation analysis linked candidate genera and metabolites with rumen fermentation and selected serum biochemical parameters. Overall, 0.5% YC partially alleviated high-concentrate diet-induced rumen acidification and was associated with improved microbial and metabolic homeostasis.