Compound Enzyme Supplementation Improves Intestinal Health, Immunity, and Antioxidant Capacity in Pigeons via Gut Microbiota and Metabolome Modulation

The study evaluated the effects of dietary compound enzyme preparations (CEPs) supplementation on antioxidant capacity, immune response, and intestinal health of pigeons. A total of 288 White King parent pigeons were randomly assigned to four treatments, with six replications of 12 pigeons each. The control (CK) group received a basal diet, whereas the CEP groups were fed a basal diet with 0.25 g/kg (low compound enzyme preparation group, LCEP), 0.5 g/kg (middle compound enzyme preparation group, MCEP), and 1.0 g/kg (high compound enzyme preparation group, HCEP) CEPs. Results showed that supplementation with 0.25 g/kg of CEPs significantly increased duodenal crypt depth (CD), as well as jejunal villus height (VH) and the villus height-to-crypt depth ratio (VCR) (p < 0.05). It also increased the immunoglobulins of serum, such as IgA, IgG, and IgM, as well as enhanced antioxidant capacity by increasing superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities of serum (p < 0.05). Furthermore, we found that CEPs altered ileum content microbiota composition, increasing the relative abundance of p_Bacteroidota and g_Bifidobacterium (p < 0.05). In addition, untargeted metabolomics analysis identified 92 upregulated and 95 downregulated metabolites. Pathway enrichment analysis of these differential metabolites revealed that CEP supplementation altered the metabolomic profile of the ileum contents, with differential metabolites mainly enriched in alanine, aspartate and glutamate metabolism, fatty acid biosynthesis, and unsaturated fatty acid biosynthesis pathways. These results demonstrated that dietary supplementation with CEPs at different doses improved antioxidant capacity to varying degrees and maintained intestinal immune balance by modulating microbiota, which provides a theoretical basis for the rational application of compound enzyme preparations in breeding pigeon feed. Moreover, this study provides mechanistic evidence that CEPs can improve intestinal health, immunity, and antioxidant capacity. It also fills a key knowledge gap in pigeon nutrition by linking enzyme use with gut microbiota and metabolic regulation.