Abstract
Skeletal muscle fiber composition strongly influences meat quality and metabolic regulation in poultry, yet fiber-type-specific responses to high-fat diet (HFD) remain poorly understood. Here, we investigated the effects of short-term and long-term HFD feeding on the fast/glycolytic pectoralis major (PEM) and slow/oxidative soleus (SOL) in Guangyuan Grey chickens. Histological staining and enzyme activity assays revealed that prolonged HFD promoted an oxidative-to-glycolytic transition in SOL, accompanied by reduced mitochondrial function, whereas the PEM showed early lipid accumulation and metabolic stress. Transcriptome sequencing identified 3840 differentially expressed genes between the two muscles, with 1761 constitutively different. Under short-term HFD, SOL activated protective pathways including PPAR and autophagy, while PEM showed limited adaptation. Long-term HFD induced further downregulation of fatty acid metabolism and structural genes (e.g., PM20D2, SLC27A1, and GADD45G) in PEM, but SOL maintained or enhanced expression of genes (e.g., NR4A3, PPARA, and SLC6A6) involved in muscle organization and lipid processing. Temporal clustering highlighted progressive divergence in transcriptional responses. These results suggest SOL fibers exhibit greater resilience to lipid overload than PEM fibers. Our findings provide insight into the molecular basis of muscle-type-specific adaptations to dietary fat and offer targets for improving metabolic health and meat quality in poultry.