The Effects of Cysteamine Zinc Supplementation on Blood Hormones, Intestinal Flora, and Metabolites in Lactating Mares

This study aimed to investigate the effects of cysteamine zinc (CS-Zn) supplementation on blood biochemical indices, blood hormones, fecal fermentation, fecal microbial diversity, and blood metabolites in lactating mares. Blood samples were collected via jugular venipuncture, and fecal samples were collected via rectal sampling before morning tethering on days 30, 60, and 90 of the trial. Fecal samples were analyzed for volatile fatty acids (VFAs) and microbial diversity, while changes in blood biochemical indices, blood hormones, and blood non-targeted metabolomics were also analyzed. The results showed that compared with the control group, the test group exhibited significant increases in total protein, globulin, urea, and glucose in the blood (p < 0.05); growth hormone (GH) levels significantly increased, while somatostatin levels significantly decreased (p < 0.05); and concentrations of all VFAs in feces significantly increased (p < 0.05). Simultaneously, CS-Zn supplementation significantly reduced the relative abundance of Family_XIII_UCG-001, Monoglobus, and UCG-007 at the genus level. Metabolomics analysis revealed that differentially expressed metabolites were enriched in pathways such as neuroactive ligand–receptor interaction, phenylalanine, tyrosine and tryptophan biosynthesis, and dopaminergic synapse, with significant upregulation of L-tyrosine and dopamine in the blood. These findings indicate that CS-Zn supplementation, on the one hand, can enhance pathways such as glucose metabolism, tyrosine metabolism, and bile secretion by depleting somatostatin and increasing growth hormone levels, and on the other hand, it can improve energy metabolism in mares by altering intestinal microbiota structure and enhancing fiber fermentation efficiency.