Effects of probiotic-fermented milk thistle meal on dairy goat production, milk quality, serum biochemistry, and rumen-fecal metagenomes

Milk thistle meal (MTM), a protein-rich byproduct, is underutilized despite large-scale production. In this study, we evaluated Bacillus subtilis , Limosilactobacillus reuteri , and Saccharomyces cerevisiae co-fermented MTM (FMTM) on dairy goat performance, milk quality, antioxidant status, and microbial community, replacing soybean meal at 0 % (CON), 50 % (FMTM0.5), or 100 % (FMTM), MTM replacing soybean meal at 100 % was also tested. The FMTM0.5 significantly increased milk yield compared to CON ( P < 0.05). Additionally, serum total protein and globulin levels rose in FMTM groups ( P < 0.05), indicating improved nutritional status. Antioxidant capacity improved in FMTM-fed goats ( P < 0.05), evidenced by reduced oxidative stress markers and elevated antioxidant enzyme activity. Rumen total volatile fatty acids, acetate, propionate, and butyrate increased notably with FMTM0.5 ( P < 0.05). Metagenomic analysis revealed FMTM enriched beneficial rumen bacteria (e.g., Prevotella ), suppressed methanogens, and upregulated carbohydrate/fiber-degrading genes, suggesting enhanced feed efficiency and reduced methane emissions. These findings highlight the potential of FMTM in dairy goat production, revealing its role in regulating gastrointestinal microbiota and suggesting novel strategies for the reutilization of herbal residues.