Supplementation of Bacillus coagulans and Tributyrin to Danzhou Chickens: Effects on Growth Performance, Antioxidant Status, Immune Response, Intestinal Health, and Cecal Microbiome

To investigate the effects of <i>Bacillus coagulans</i> (BC) and tributyrin (TB) on Danzhou chickens, a 2 × 2 factorial design was adopted. A total of 480 chickens were randomly assigned to four dietary treatments, consisting of two BC levels (0 and 1.5 g/kg) and two TB levels (0 and 1.0 g/kg), for a 35-day trial. The results showed that supplementation with BC or TB alone significantly increased the average daily gain (ADG), serum immune parameters (immunoglobulin A, immunoglobulin G, and anti-inflammatory cytokines interleukin-4 and interleukin-10), total antioxidant capacity, and catalase activity, while reducing pro-inflammatory cytokine levels and the feed-to-gain ratio (<i>p</i> < 0.05). In addition, individual supplementation with BC or TB also enhanced digestive enzyme activities in the intestine, increased villus height in the small intestine, and optimized the structure of the cecal microbiota (<i>p</i> < 0.05). More importantly, significant synergistic interactions between BC and TB were observed across multiple parameters (<i>p</i> < 0.05). Combined supplementation further increased ADG, serum immunoglobulin M levels, superoxide dismutase activity, lipase activity in the ileum, and villus height in the jejunum (<i>p</i> < 0.05). Meanwhile, the combined supplementation also significantly elevated the abundance of beneficial bacteria such as <i>Bacteroides</i>, <i>Eubacterium_brachy_group</i>, and <i>Negativibacillus</i>. In conclusion, supplementation with BC or TB effectively improved the growth performance, antioxidant status, immune function, intestinal morphology, and cecal microbiota composition of Danzhou chickens, and the combined supplementation demonstrated superior effects compared to individual supplementation.