Yeast Culture Enhances Production Performance in Late-Lactation Dairy Cows by Reshaping Rumen Microbiota and...

Yeast culture (YC), a complex functional feed additive containing fermentation metabolites, has demonstrated potential in dairy production systems. However, its mechanistic effects on rumen function and host metabolism in lactating dairy cattle warrant further investigation. This study evaluated the impacts of YC supplementation on production performance, systemic antioxidant status, and rumen function in late-lactation Holstein cows. Fourteen multiparous Holstein cows (body weight 655 ± 28 kg; days in milk 270.4 ± 1.6 d) were randomly allocated into two groups, a control group (CON, basal diet) and a YC-supplemented group (YC, basal diet + 50 g/d YC), in a 28-day feeding trial. YC supplementation significantly increased dry matter intake (p < 0.01), nutrient digestibility (p < 0.01 for DM, CP, EE, NDF, and ADF), and milk yield (p < 0.05) compared to CON. Systemic antioxidant capacity was enhanced, as evidenced by elevated serum superoxide dismutase activity (p < 0.01) and total antioxidant capacity (p < 0.05). Rumen fermentation was improved with higher concentrations of total volatile fatty acids (p < 0.01) and microbial protein (p < 0.01) and reduced ammonia nitrogen levels (p < 0.01). Macrogenomic analysis revealed a YC-mediated restructuring of the rumen microbiota, characterized by an increased relative abundance of Firmicutes and decreased Bacteroidota. Untargeted metabolomic profiling identified significant alterations in rumen metabolite profiles, with differential metabolites enriched in pyrimidine metabolism and vitamin digestion and absorption pathways. These results indicate that YC supplementation improves production performance in late-lactation dairy cows through multi-faceted mechanisms involving rumen microbial community modulation and metabolic pathway activation, ultimately enhancing nutrient utilization and metabolic efficiency.