Combination Effects of Bacillus subtilis and Chito-Oligosaccharides on Antioxidant Function, Immune Function and Intestinal Barrier Function in Broilers

This study aimed to investigate the regulatory effects of combined Bacillus subtilis (BS) and chito-oligosaccharides (COS) supplementation on growth performance, antioxidant function, immune function, and intestinal barrier function of broilers. A total of 288 one-day-old broilers were randomly assigned to six groups, each consisting of six replicates of eight broilers. The control group was fed a basal diet (CON group). The experimental groups were fed the basal diet supplemented with 5 × 109 CFU/kg BS (BS1 group), 6 × 109 CFU/kg BS (BS2 group), 125 mg/kg COS (COS group), 5 × 109 CFU/kg BS + 125 mg/kg COS (MIX1 group) and 6 × 109 CFU/kg BS + 125 mg/kg COS (MIX2 group). The 42-day experiment consisted of two periods: a starter period (days 1–21) and a grower period (days 22–42). BS, COS and their combinations increased BW at 21 days (p < 0.05). The BS2, COS, MIX1, and MIX2 groups improved the average daily gain (ADG) during days 1–21 (p < 0.05). COS significantly reduced the feed conversion ratio (FCR) over 42 days (p < 0.05). For antioxidant function, MIX2 decreased serum MDA, while MIX1 increased hepatic GSH content, GSH-Px activity, and T-AOC (p < 0.05). MIX1 upregulated hepatic CAT, GPX, SOD, and HO-1 mRNA expression and jejunal SOD expression (p < 0.05). For immune function, BS1 decreased jejunal IL-1β and IL-4 and increased IL-10 (p < 0.05), whereas MIX1 increased serum and hepatic IL-1β and IL-4 (p < 0.05). BS1 showed the highest hepatic IL-10 expression, while MIX1 upregulated NFKB1 and RELA (p < 0.05). For intestinal barrier, COS and MIX1 upregulated JAM-2, and BS1, MIX1, and MIX2 increased Occludin, with MIX2 showing the highest ZO-1 expression (p < 0.05). In conclusion, dietary supplementation with BS and COS, either alone or in combination, can improve the growth performance, antioxidant function, immune function, and intestinal barrier function of broilers to varying degrees, with evident dose dependency and tissue specificity.