Effects of  chlorogenic acid on growth performance, immunity, antioxidant capacity, intestinal microbiota, and liver transcriptome in  Mauremys mutica
This study investigated the impact of chlorogenic acid (CGA) as a dietary supplement on yellow pond turtles (Mauremys mutica) and five separate groups were conducted (0 mg/kg , Con; 100 mg/kg, CGA1; 200 mg/kg, CGA2; 400 mg/kg, CGA4; 800 mg/kg, CGA8). Compared to the control group, CGA supplementation at concentrations ranging from 100 to 800 mg/kg significantly enhanced final body weight, weight gain rate, and specific growth rate, while reducing feed conversion rate (P < 0.05). Furthermore, CGA improved intestinal digestive enzyme activities (amylase, lipase, and trypsin), promoted intestinal morphological development, and increased villus length and density. Serum levels of alkaline phosphatase (AKP), acid phosphatase (ACP), complement C3, and complement C4 were elevated, while superoxide dismutase (SOD) and catalase (CAT) activities increased. Malondialdehyde (MDA) levels decreased in all experimental groups. Notably, the 200 mg/kg CGA treatment exhibited the most significant improvements in growth performance, digestive enzyme activity, intestinal morphology, villus length, immunity, and antioxidant capacity. Transcriptomic analysis revealed that CGA influenced liver gene expression, with the 200 mg/kg CGA group showing the greatest number of differentially expressed genes (DEGs). Key genes, such as MHC I and MHC II, were significantly downregulated and enriched in KEGG pathways related to Th1 and Th2 cell differentiation, Th17 cell differentiation, asthma, and other immune-inflammatory conditions. These differentially expressed genes and enriched pathways were closely linked to immune responses and inflammatory processes. Additionally, CGA supplementation increased the relative abundance of Cetobacterium and reduced the abundance of Escherichia_Shigella and Treponema in the intestinal microbiota. In conclusion, CGA supplementation improves growth performance, intestinal morphology, and digestive enzyme activity in yellow pond turtles, enhances immunity and antioxidant capacity, and optimizes the intestinal microbiota. Based on these findings, a CGA supplementation level of 200 mg/kg is recommended for M. mutica diets.