Effects of Adding <i>Bacillus coagulans</i> BCH0 to the Diet on Growth Performance, Tissue Structures, and Gut Microbiota in Broilers

Studies demonstrated that <i>Bacillus coagulans</i> (<i>B. coagulans</i>) as a dietary additive enhanced broiler growth performance, yet its mechanisms of action modulation remained unclear. Therefore, this study investigated effects of dietary <i>B. coagulans</i> BCH0 (1 × 10⁹ CFU/kg) on growth performance, intestinal morphology, gut microbiota, and ileal transcriptomics in Arbor Acres broilers using a completely randomized design. A total of 200 one-day-old broilers were allocated to control (Con, basal diet) and experimental (BCH0, basal diet + 1 × 10⁹ CFU/kg <i>B. coagulans</i> BCH0) groups (10 replicates/group, 10 birds/replicate) over a 42-day trial. The results revealed that BCH0 significantly increased body weights (BW) at 21 and 42 days (<i>p</i> < 0.05), improved the average daily gain (ADG) during the starter (1–21 days) and overall phases (1–42 days), and reduced the ratio of feed intake to body weight gain (F/G) across all phases (<i>p</i> < 0.05). Duodenal morphology analysis indicated a BCH0 elevated villus height (+16.9%, <i>p</i> < 0.01) and villus height/crypt depth (V/C) (<i>p</i> < 0.01) and no significant differences in crypt depth (<i>p</i> = 0.46). In the ileum, the BCH0 group exhibited a significantly greater villus height (<i>p</i> < 0.01), crypt depth (<i>p</i> < 0.05), and V/C (<i>p</i> < 0.05) than the Con group. Microbiota analysis revealed no significant differences in α-diversity or β-diversity, but phylum-level shifts involved an increase in <i>Firmicutes</i> and a reduction in <i>Actinobacteriota</i> in the BCH0 group. At the genus level, dominance shifted from <i>Romboutsia</i> (Control group) to <i>Lactobacillus</i> (BCH0 group), accompanied by marked reductions in <i>Turicibacter</i>, <i>Ldatus_arthromitus</i>, and <i>Rothia</i>. Ileal transcriptomics identified 605 differentially expressed genes, with KEGG enrichment highlighting activated nutrient assimilation pathways (<i>p</i> < 0.05), including carbohydrate, mineral, fat, and protein digestion/absorption. These findings collectively demonstrated that <i>B. coagulans</i> BCH0 enhanced broiler growth through the synergistic modulation of beneficial microbiota, the upregulation of nutrient metabolism genes, and intestinal architectural optimization, supporting its role as a sustainable microbial additive for enhancing poultry productivity and gut health.