Muscle Metabolomic Responses of Dumont and Mongolian Sheep to Alfalfa Hay- and Corn Straw-Based Diets: An Untargeted Metabolomics Study

This study evaluated the effects of forage source on the longissimus dorsi muscle metabolomic profiles of Dumont and Mongolian sheep. A total of 24 male sheep, including Dumont sheep (DS) and Mongolian sheep (MS), were assigned to a 2 × 2 factorial design with two breeds and two forage sources: alfalfa hay (AH) and corn straw (CS). The four groups were DSAH, DSCS, MSAH, and MSCS, with six lambs per group. Untargeted metabolomics was used to characterize muscle metabolic profiles after a 90-day feeding period. Stable metabolomic separations were mainly observed between forage treatments within each breed, namely DSAH vs. DSCS and MSAH vs. MSCS, whereas breed comparisons under the same forage condition showed limited separation and weaker model stability. OPLS-DA combined with univariate analysis identified 101 and 100 differential metabolites in the DSAH vs. DSCS and MSAH vs. MSCS comparisons, respectively. Pathway enrichment analysis indicated that forage-associated metabolic differences were mainly related to amino acid metabolism, lipid metabolism, and energy metabolism. AH feeding was associated with broader changes in muscle metabolic pathways than CS feeding, particularly in pathways related to nutrient utilization and lipid-related metabolism. These findings suggest that the forage source is closely associated with muscle metabolic variation in fattening lambs, while possible breed-related differences in metabolic responsiveness require further validation.