Transcriptomic Analysis of Skeletal Muscle Biochemical Adaptation to Chronic Heat Stress in Commercial Broiler Chickens: Implications for Production under Nigerian Tropical Conditions

Chronic heat stress in commercial broilers impairs muscle growth through complex biochemical adaptive mechanisms that extend beyond classical thermotolerance responses, and a transcriptome-wide characterisation of skeletal muscle adaptation to chronic thermal challenge in tropical Nigerian conditions has not been conducted. This doctoral study applied RNA sequencing and targeted metabolomics to characterise skeletal muscle biochemical adaptation to chronic heat stress in commercial Arbor Acres broilers maintained under simulated northern Nigerian hot-dry season conditions at the National Veterinary Research Institute, Vom, Plateau State, North Central Nigeria. One hundred and twenty broilers at two weeks of age were allocated to thermoneutral (22 degrees Celsius) and chronic heat-stressed (35 degrees Celsius) chambers for five weeks. Pectoralis major muscle samples collected at the terminal phase were subjected to RNA sequencing, targeted amino acid metabolomics, and enzyme activity assays for key glycolytic and mitochondrial enzymes. Heat-stressed broilers showed significant transcriptomic downregulation of myosin heavy chain isoforms and upregulation of heat shock protein 70 and ubiquitin-proteasome pathway genes, consistent with proteolytic muscle catabolism. Amino acid metabolomics confirmed branched-chain amino acid depletion and elevated alanine in heat-stressed muscle, implicating enhanced gluconeogenic substrate provision. Mitochondrial cytochrome c oxidase activity was significantly reduced in heat-stressed broilers. Integration of transcriptomic and metabolomic data through pathway analysis identified muscle atrophy signalling, impaired mitochondrial biogenesis, and heat shock response as the dominant adaptive pathways. These original multi-omic contributions advance understanding of tropical heat stress muscle biochemistry and provide actionable targets for feed additive and genetic selection strategies in Nigerian commercial poultry. Keywords: heat stress, skeletal muscle, transcriptomics, broilers, heat shock protein.