Effects of variable incubation temperature during embryonic days 10-13 on leg muscle transcriptomics in day-old broiler and layer chicks.

In chickens, secondary myogenesis occurs during embryonic days (ED) 10-13, which is a critical developmental window sensitive to incubation temperature as a key environmental factor. This study investigates transcriptional profiles in leg muscle of broiler (Ross 308; Ross) and layer chickens (Lohmann Brown; LB) at hatch following transient ± 1 °C deviations from standard incubation temperature during ED 10-13. Eggs were incubated at 37.8 °C (CON), 36.8 °C (Low), or 38.8 °C (High) for 72 h between ED 10-13 before being returned to standard conditions until hatch (ED 21). Leg muscle samples from both sexes were analysed using RNA sequencing (n = 108). Hatch body weight and yolk-free body weight were higher in Ross compared to LB, but were unaffected by incubation temperature. Lowered incubation temperature in LB hatchlings was associated with altered mitochondrial and metabolic pathways, including the downregulation of genes involved in oxidative phosphorylation and reduced expression of myogenic regulators such as MYF5 and MYOG compared to CON birds. Increased incubation temperature involved enrichment of proteolytic processes and downregulation of genes associated with extracellular matrix organization (COL1A1, COL6A1) in LB hatchlings and myogenesis (MYOG) in Ross hatchlings compared to CON birds. Results suggest that deviations from standard incubation temperature during the critical window of secondary myogenesis modulate leg muscle development in a strain-specific manner.