Effects of Dietary Bacillus subtilis HC6 on Growth Performance, Antioxidant Capacity, Immunity, and Intestinal Health in Broilers

SIMPLE SUMMARY: In the post-antibiotic era, the attainment of higher feed efficiency has become the primary goal of the poultry farming. Bacillus subtilis is commonly used as a substitute for antibiotics in animal and poultry feed. The results demonstrated that dietary 5 × 10(8) cfu/kg Bacillus subtilis HC6 increased the feed efficiency, antioxidant capacity, and mRNA expression of pro-inflammatory cytokines in the jejunal mucosa, and decreased the activity of diamine oxidase in serum, which might be attributed to the modulation of community composition and functions of cecal microbiota in white-feathered broilers. Our results provide new insights and evidence for the application of probiotics in broiler breeding. ABSTRACT: This study aimed to investigate the impact of Bacillus subtilis HC6 on the growth performance, immunity, antioxidant capacity, and intestinal health of broilers. A total of 180 one-day-old white feather broilers were randomly divided into two experimental groups, each comprising six replicates of fifteen chicks from 1 to 50 d of age. The groups were either fed a basal diet (CON) or the same diet supplemented with 5 × 10(8) cfu/kg of Bacillus subtilis HC6 (BS). Our results indicated that compared with the CON, dietary supplementation with BS increased feed efficiency during d 21–50 and d 1–50 (p < 0.05). Moreover, BS supplementation enhanced antioxidant capacity in the serum and liver, and also decreased the activity of diamine oxidase and the level of endotoxins (p < 0.05). Additionally, BS treatment increased the villi height in the jejunum and ileum, increased the ratio of villus height/crypt depth in the ileum, upregulated the expression of tight junction proteins in the jejunal mucosa, and downregulated the levels of IL-22 and IFN-γ on day 50 (p < 0.05). Principal coordinates analysis yielded clear clustering of two groups; dietary BS increased the relative abundance of Bacteroidales_unclassified (genus) and Olsenella (genus), and decreased the abundance of genera Alistipes on day 50, which identified a strong correlation with FCR, serum differential metabolites, or differential gene expression in the jejunal mucosa by spearman correlation analysis. The PICRUSt2 analysis revealed that supplementation with BS enriched the pathways related to xenobiotics biodegradation and metabolism, carbohydrate metabolism, energy metabolism, signaling molecules and interaction, the digestive system, and transport and catabolism. These results demonstrated that dietary BS increased feed efficiency, antioxidant capacity, and the mRNA expression of pro-inflammatory cytokines in the jejunal mucosa; and decreased the activity of diamine oxidase in serum, which might be attributed to the modulation of community composition and the functions of cecal microbiota in white-feathered broilers.