Effects of rumen-protected valine supplementation on velvet antler growth, faecal microbiota, serum metabolites, and velvet antler gene expression in sika deer

This study evaluated the effects of rumen-protected valine supplementation on velvet antler growth and examined the associated changes in faecal fermentation, serum metabolism, and antler gene expression in sika deer. Twenty-one 2-year-old male sika deer were randomly assigned to control (Con), low-valine (LVal; 1 g/d), and high-valine (HVal; 3 g/d) groups. Rumen-protected valine supplementation increased antler weight and average daily antler weight gain ( P < 0.05), with the strongest response in LVal. LVal also increased faecal total volatile fatty acids, propionate, and serum glucose, and altered the faecal bacterial community structure, including increased abundance of Clostridium sensu stricto 1 and Turicibacter . Targeted serum metabolomics identified valine-responsive metabolites related to energy and nucleotide metabolism, including myo-inositol, xylulose-5-phosphate, creatinine, xanthosine, and N-acetylneuraminic acid. Transcriptome analysis showed that the cartilage (CA) layer exhibited the strongest transcriptional response, with differentially expressed genes enriched in nucleotide sugar biosynthesis, insulin and AMPK signalling, and extracellular matrix organisation. Weighted gene co-expression network analysis (WGCNA) identified a CA-layer gene module associated with velvet antler weight and several serum metabolites, while correlation analysis revealed positive pairwise associations among N-acetylneuraminic acid, CDH17 expression, and velvet antler weight. These findings indicate that rumen-protected valine supplementation promoted velvet antler growth and was accompanied by coordinated changes in faecal fermentation, serum metabolism, and CA-layer gene expression.