Influence of incubation temperature on embryonic Days 4–7 on gene expression, <i>M. pectoralis</i> and <i>M. gastrocnemius</i> microstructure, and tibia characteristics in Ross 308 Broilers

The incubation temperature can influence chicken bone and muscle development, and breast and leg muscles may respond differently to changes therein. Ross 308 broiler eggs were incubated at 36.5°C, 37.5°C (control), 38.5°C and 39.0°C on embryonic days 4–7. M. pectoralis and M. gastrocnemius were sampled at hatching and 5 weeks post-hatching, and differences in gene expression, microstructure and energy metabolism were examined. Tibia strength was tested, and gait scoring was performed. Broiler performance was similar at slaughter age, but initial growth was slowed by the 36.5°C treatment. The 38.5°C treatment reduced the M. gastrocnemius weight and shifted the M. pectoralis/M. gastrocnemius ratio. All treatments reduced M. gastrocnemius glycogen content relative to the control. The expression of single myogenesis-related genes was altered in the M. pectoralis by 36.5°C. The results indicate that the incubation temperature influences broiler muscle energy metabolism, and that the temperature of 38.5°C hampers leg muscle development.