Bacillus Subtilis LN077 as a Probiotic Feed Additive Improves Goat Growth, Immunity, and Rumen Health.

With the transition from grazing to stall-feeding due to overgrazing and pasture limitations, antibiotics are often overused in intensive goat farming to control diseases and promote growth. However, this practice contradicts the concept of antibiotic-free livestock production. Therefore, effective alternatives are urgently needed to reduce antibiotic usage while ensuring healthy growth. To explore the application of probiotics in animal feed, we selected 3-month-old healthy male Yudong black goats with similar body weights (18.61 ± 0.61 kg). They were randomly divided into two groups: a control group (CON) fed a basal diet and a probiotic group (PRO) supplemented with 1 mL of Bacillus subtilis LN077 per kilogram of feed (as-fed basis) for 60 days. Compared with the CON group, the PRO group presented significantly greater FW and ADG (P < 0.05). Serum T-SOD, GSH-Px activity, T-AOC, and IgG levels were significantly increased, whereas IL-6 and TNF-α levels were significantly decreased (P < 0.05). The rumen NH₃-N concentration significantly decreased, whereas the acetate and total VFA concentrations significantly increased in the PRO group (P < 0.05). B. subtilis LN077 supplementation significantly altered the rumen microbiota composition, increasing the relative abundances of Chloroflexi, Patescibacteria, Clostridia UCG-014, Candidatus Saccharimonas, Bifidobacteriaceae, and Ruminococcaceae (P < 0.05) while decreasing the abundances of Bacteroidota, Verrucomicrobiota, Selenomonas, Eubacterium coprostanoligenes group, and WCHB1-41 (P < 0.01). Metabolomic analysis revealed 1,281 differentially expressed metabolites between the CON and PRO groups, including 674 upregulated and 607 downregulated metabolites. These metabolites were enriched mainly in arachidonic acid metabolism, glutathione metabolism, and phenylalanine metabolism. Furthermore, we identified several microbially derived metabolites, including dihydroceramide, bufotenin, N8-acetylspermidine, N1-acetylspermine, spermidine, theophylline, 6-carboxy-5,6,7,8-tetrahydropterin, pentadecanal, N-alpha-acetyl-L-citrulline, and octopine, and we elucidated their potential relationships with growth performance and the rumen microbiota. This study revealed potential microbe‒metabolite‒host interactions, providing new insights into the role of B. subtilis LN077 in regulating rumen health. These findings suggest that B. subtilis LN077 improves rumen fermentation, immune function, and growth performance by modulating the rumen microbiota and its metabolites. Its application may serve as a promising strategy to reduce antibiotic dependence in goat production.