Responses of Intestinal Antioxidant Capacity, Morphology, Barrier Function, Immunity, and Microbial Diversity to Chlorogenic Acid in Late-Peak Laying Hens

This study examined the influence of chlorogenic acid (CGA) on gut antioxidant status, morphology, barrier function, immunity, and cecal microbiota in late-peak laying hens. A total of 240 Hy-Line Brown hens, aged 43 weeks, were randomly assigned to four groups, the basal diet +0, 400, 600, and 800 mg/kg CGA, for 12 weeks. The results revealed that CGA significantly reduced ileal H₂O₂ and malondialdehyde levels; increased duodenal height, ileal villus height, and villus height-to-crypt depth ratio; while decreasing jejunal crypt depth. The 600 and 800 mg/kg CGA significantly upregulated the duodenal, jejunal, and ileal ZO-1 and occludin gene expression; increased IgG levels in serum and ileum; and upregulated ileal IgA gene expression. The 600 mg/kg CGA significantly upregulated CD3D and CD4 gene expression, while downregulating IL-1β gene expression in duodenum, jejunum, and ileum. Moreover, CGA changed the gut microbiota structure. The SCFA-producing bacteria <i>unclassified_f__Peptostreptococcaceae</i>, <i>unclassified_f_Oscillospiraceae</i>, <i>Pseudoflavonifractor</i>, <i>Lachnospiraceae_FCS020_group</i>, <i>Oscillospira</i>, <i>Elusimicrobium</i>, <i>Eubacterium_ventriosum_group</i>, <i>Intestinimonas</i>, and <i>norank_f_Coriobacteriales_Incertae_Sedis</i> were significantly enriched in the 400, 600, and/or 800 mg/kg CGA groups. The bacteria <i>Lactobacillus</i>, <i>Bacillus</i>, and <i>Akkermansia</i> were significantly enriched in the 600 mg/kg CGA group. Conclusively, dietary CGA (600-800 mg/kg) improved intestinal antioxidant status, morphology, barrier and immune function, and beneficial microbiota growth in late-peak laying hens.