Dietary probiotic based on a dual-strain Bacillus subtilis improves immunity, intestinal health, and growth performance of broiler chickens

The study investigated the effects of dietary probiotic of dual-strain Bacillus subtilis on production performance, intestinal barrier parameters, and microbiota in broiler chickens. In a randomized trial, male broiler chickens were allocated into 3 groups, a control group (basal diet), BS300 group (basal diet with 300 mg/kg of B. subtilis), and BS500 group (basal diet with 500 mg/kg of B. subtilis). The inclusion of 500 mg/kg of B. subtilis significantly reduced the feed conversion ratio by 4.55% during the starting phase. Both 300 and 500 mg/kg of B. subtilis supplementation increased jejunal villus height (by 17.89% and 24.8%, respectively) significantly and decreased jejunal crypt depth (by 27.2% and 31.9%, respectively) on day 21. The addition of 500 mg/kg of B. subtilis significantly elevated the gene expression of occludin on day 35. Moreover, of B. subtilis supplementation enhanced cytokine levels and immunoglobulins in both serum and jejunal mucosa. Microbial analysis indicated that B. subtilis increased the abundance of potential probiotics (Sutterella) and butyrate-producing bacteria (Lachnoclostridium, Tyzzerella, Anaerostipes, Clostridium_sensu_stricto_13, Prevotellaceae_NK3B31_group, and Lachnospiraceae_UCG-010). The abundances of Anaerostipes and Sutterella, are significantly correlated with growth performance and immune function. In conclusion, dietary supplementation with B. subtilis improved the growth performance, potentially through the regulation of immunity, intestinal barrier function, and microbiota in broilers. Notably, 500 mg/kg of B. subtilis exhibited more benefits for broilers compared to the 300 mg/kg. This research highlights the efficacy of dual-strain Bacillus subtilis in improving feed conversion, intestinal morphology, immune function, and the gut microbiota in broiler chickens under the conditions of this experiment. Bacillus emerges as a promising probiotic candidate, offering a suitable alternative to antibiotics in animal feed. However, previous research predominantly focused on single-strain Bacillus, with limited exploration into dual-strain Bacillus subtilis-based probiotics. This study demonstrates that dietary supplementation with dual-strain B. subtilis enhances feed conversion ratio, intestinal morphology, gene expression related to tight junction proteins, Th1-like cytokines, immunoglobulins, as well as the abundance of potential probiotics (Sutterella) and butyrate-producing bacteria (Anaerostipes, Tyzzerella, UCG-010, etc.) in the cecum. The abundances of Anaerostipes and Sutterella, are significantly correlated with growth performance and immune function. These findings lay a foundation for incorporating dual-strain B. subtilis-based probiotics in broiler feed.