Bacillus affects Taihe Silky Fowls growth performance, cecal microbiota, and metabolite during growing period

Bacillus, a well-recognized probiotic genus, regulates intestinal microbiota to maintain gut homeostasis and enhance host immunity. Taihe Silky Fowl (Taihe SF)-a high-quality Chinese indigenous chicken breed-has poor disease resistance, limiting its commercial farming efficiency. This study evaluated the effects of four strains (Bacillus subtilis, Bacillus coagulans, Bacillus licheniformis, Clostridium butyricum) on growth performance, antioxidant capacity, intestinal barrier integrity, and cecal microbiota of 3-13-week-old Taihe SF, to identify the optimal strain for this stage. 1,200 3-week-old Taihe SF, with close body weights (45.2 ± 2.1 g, P > 0.05) and health status were randomly divided into 5 groups (6 replicates/group, 40 birds/replicate). Four experimental groups received diets supplemented with B. subtilis, B. coagulans, B. licheniformis, or C. butyricum (10¹⁰ CFU/g, 1000 mg/kg). It was observed that four experimental groups remarkedly decreased (P < 0.05) the feed conversion ratio in Taihe SF from 3 to 13 weeks. The catalase, total antioxidant capacity, and total superoxide dismutase levels in serum experienced a significant rise (P < 0.05) in the BS and CB groups, compared with the CON group, while the content of malondialdehyde significantly decreased (P < 0.05). Compared with CON group, all four experimental groups significantly increased the villus length and reduced the crypt depth in the jejunum (P < 0.05). The level of diamine oxidase in the jejunum saw a notable decline (P < 0.05), and there was an increase in the relative mRNA expression of Occludin, Claudin-1, Claudin-2, and zonula occludens1 within the jejunum. Furthermore, the BS group exhibited a significant enhancement in the relative abundance of Firmicutes in the cecum, accompanied by a marked reduction in the relative abundances of Bacteroidota and Proteobacteria. B. subtilis also led to an elevation of indole-3-propionic acid concentrations in the intestines of Taihe SF. Based on these findings, B. subtilis is deemed the most advantageous among the tested strains for Taihe SF during the 3-13 week growth period.