Effects of Dietary Zinc Cysteamine Supplementation on Growth Performance, Physiological Responses, and Fecal Microbiota in Weaned Foals

Zn-CS chelate has shown beneficial effects on gut health and growth in piglets, but its impact on weaned foals remains largely unknown. This study evaluated the effects of dietary Zn-CS supplementation on growth performance, nutrient digestibility, physiological status, and fecal microbiota in weaned Ili foals. Thirty-two six-month-old foals were randomly assigned to four treatment groups receiving 0, 2, 4, or 6 mg Zn-CS/kg body weight per day for 90 days. Growth performance, nutrient digestibility, plasma biochemical parameters, liver function enzymes, serum hormones, antioxidant indices, fecal pH, volatile fatty acids, and fecal microbial composition were measured. Dietary Zn-CS supplementation significantly increased final body weight, total weight gain, and average daily gain (p < 0.05), while linearly improving body size indicators. Apparent digestibility of dry matter, digestible energy, metabolizable energy, and acid detergent fiber was markedly enhanced (p < 0.05). Zn-CS supplementation also effectively regulated plasma albumin and total cholesterol levels and hepatic enzyme activities, and strongly enhanced antioxidant function by increasing superoxide dismutase, glutathione peroxidase, catalase activities, and total antioxidant capacity, while reducing malondialdehyde content (p < 0.01). Additionally, Zn-CS upregulated plasma growth hormone, insulin, and triiodothyronine concentrations, decreased somatostatin secretion (p < 0.05), reduced fecal pH, and increased VFA contents. Notably, Zn-CS reshaped the fecal microbial structure by increasing beneficial bacteria and inhibiting potential pathogens. In conclusion, dietary Zn-CS supplementation effectively promotes growth and health in weaned Ili foals, with 6 mg/kg BW/day being the optimal supplemental dose under experimental conditions.