Bacillus and Lactobacillus synergy in low-protein diets boosts growth performance and reduces nitrogen emissions in finishing pigs.

BACKGROUND: Low-protein diets can reduce nitrogen losses in pig production, but complementary strategies are needed to maintain productivity. This study evaluated whether supplementation with a fermentation mixture of Bacillus subtilis and Lactobacillus acidophilus (FAM) improves growth performance, nitrogen utilization, and nitrogen emission in finishing pigs. RESULTS: A total of 180 crossbred Duroc × Landrace × Yorkshire finishing pigs with an initial body weight of 100.01 ± 8.39 kg were randomly allocated into three groups, namely, Con, 153.3 g kg-1 crude protein (CP); LP, 133.7 g kg-1 CP; FAM, 133.7 g kg-1 CP + 1 g kg-1 FAM, and the test period was 49 days. Compared with the Con and LP groups, FAM supplementation increased average daily gain by 14.6% and 12.0%, respectively (P < 0.05), and decreased feed-to-gain ratio by 11.3% and 12.2%, respectively (P < 0.01). Compared to the LP group, FAM supplementation further reduced ammonia emission, serum urea nitrogen, and fecal ammonium nitrogen content (P < 0.05). Additionally, both LP and FAM groups exhibited lower muscle shear force (P < 0.01) and higher intramuscular fat content (P < 0.05) compared to the Con group. Metagenomic analysis revealed that FAM enriched Prevotella and Porphyromonadaceae and enhanced microbial pathways related to nitrogen metabolism, ATP-binding cassette transporters, amino acid transport and metabolism, and coenzyme transport and metabolism. CONCLUSION: These findings demonstrate that FAM supplementation in low-protein diets synergistically improves growth efficiency, meat quality, and environmental sustainability in pig production. © 2026 Society of Chemical Industry.