Effect of Bacillus subtilis Supplemented Diet on Broiler's Intestinal Microbiota and TLRs Gene Expression

This study aimed to investigate the effects of dietary Bacillus subtilis supplementation on gut microbiota diversity, digestive enzyme activity, and Toll-like receptor (TLR) expression in broiler chickens. A total of 240 "817" crossbred broiler chickens were randomly assigned to four groups: control (basal diet, BD), group I (BD + 300 g/d B. subtilis at 1.08 × 107 CFU/kg), group II (BD + 600 g/d B. subtilis at 2.16 × 107 CFU/kg), and group III (BD + 900 g/d B. subtilis at 3.24 × 107 CFU/kg). Gut microbiota analysis revealed significant improvements in the abundance of specific microorganisms in the treatment groups, with distinct variations in the core microorganisms between the groups. Notably, protease activity in the ileum was significantly increased in groups II (22.59%; p < 0.01) and III (14.49%; p < 0.05) compared to that in the control group. Moreover, significant up-regulation of TLR1A and TLR7 expression was observed in jejunum and cecum of the treated groups. Additionally, the TLR1B expression in the ileum was significantly increased. Furthermore, TLR2A and MyD88 transcription levels were significantly elevated in the jejunum, liver, spleen, and kidneys of experimental groups. Modulations in the expression of various TLR's (TLR2B, TLR3, TLR4, TLR15, and TLR21) were also observed in different organs. The spleen and kidney of B. subtilis-supplemented chickens exhibited upregulated expression of the proinflammatory cytokine IL-1β. Dietary supplementation with B. subtilis in broiler chickens improved the gut microbiota diversity and significantly upregulated TLR's expression in various organs. B. subtilis could be a valuable feed additive, contributing to improved disease management and overall health in broiler chickens.