Skeletal muscle exhibits coordinated metabolic adaptations toward lipid utilization and enhanced redox capacity in...

Improving feed efficiency in dairy cattle requires a better understanding of tissue-specific mechanisms that support energy and nutrient utilization. Skeletal muscle represents a major proportion of body mass in dairy cows and plays a major role in postabsorptive metabolism. Our previous liver proteomics study highlighted that high-efficiency (HE) cows exhibit enhanced hepatic fatty acid oxidation, supporting lower feed intake without compromising productivity. This study aimed to identify muscle-based metabolic adaptations associated with feed efficiency. Skeletal muscle samples from 8 HE (low residual feed intake, RFI) and 8 low-efficiency (LE; high-RFI) mid-lactation (119 ± 33 DIM) Holstein cows, ranked at the top and bottom 10% of RFI, were analyzed using tandem mass tag proteomics and quantitative real-time PCR to identify differences in skeletal muscle related to feed efficiency. The HE cows had significantly greater muscle glycogen content and exhibited a coordinated metabolic shift favoring lipid utilization. Quantitative real-time PCR showed increased expression of β-oxidation (PPARA, ACADS, ACADVL, ACOX1) and triglyceride mobilization (ATGL) in HE cows. In contrast, proteomics revealed lower abundance of glycolytic and glycogenolytic enzymes (e.g., ALDOA, PFKM, PGAM2, PYGM, AGL) in HE muscle, indicating reduced glucose and glycogen catabolism. Proteins involved in the SLC2A4 (GLUT4) translocation pathway (ACTG1, YWHAH, YWHAZ) were more abundant in HE cows, suggesting an increased capacity for insulin-stimulated GLUT4 translocation, which may contribute to greater glycogen storage. Proteomics also showed enhanced redox regulation in HE cows, with greater abundance of glutathione reductase, CAT, GPX1, and PRDX2, and lower abundance of mitochondrial complexes I (NDUFB8) and III (UQCRC2), major sites of reactive oxygen species formation. These results indicate that skeletal muscle in HE cows adopts a metabolic phenotype characterized by increased reliance on lipid-derived fuels, glucose sparing, and improved oxidative homeostasis. Together with previously reported hepatic adaptations, these muscle-specific responses likely contribute to whole-animal feed efficiency in lactating dairy cows.