Carnosine and Acyl Carnitines as Metabolic Determinants of Muscle Phenotypic Differences Between Longissimus Dorsi and Triceps Brachii in Hanzhong Sheep

Muscle traits are critical determinants of meat quality and productivity in sheep, influenced by both breed and anatomical region. Hanzhong sheep, an indigenous Chinese breed, are prized for tender, low-odor meat; yet, the molecular mechanisms underlying these traits remain poorly understood. In this study, we integrated meat quality assessment with metabolomic and transcriptomic profiling of the longissimus dorsi (HZ-B) and triceps brachii (HZ-T) muscles to elucidate biochemical and molecular bases of regional differences. The results, derived from metabolomic profiling, demonstrated that the muscle tissue of Hanzhong sheep contained abundant proteins (95 kinds) and fatty acids (150 kinds). The greater tenderness of HZ-B compared to HZ-T was associated with higher levels of dipeptides such as carnosine (FC = 1.07) and anserine (FC = 1.04), as well as upregulated expression of oxidative fiber-related genes MYH2 (FC = 2.92) and TPM1 (FC = 2.15). In contrast, HZ-T showed enrichment of flavor-associated metabolites, including acylcarnitines and glutamate, alongside higher expression of <i>FBXO32</i> (FC = 0.35) and <i>MYBPC1</i> (FC = 0.47), linked to structural integrity and muscle contraction. Integrated analysis revealed strong associations between metabolite abundance (carnosine/anserine) and key genes (<i>FBXO32</i>/<i>GADL1</i>), suggesting coordinated regulation of meat quality traits. These findings provide mechanistic insights into the metabolic and transcriptomic determinants of muscle quality in Hanzhong sheep, offering a foundation for genetic improvement and conservation strategies.