Thermal manipulation during mid-embryogenesis alters myogenic gene expression and muscle morphometry in broilers

ABSTRACT This study evaluated the effects of embryonic thermal manipulation (TM) at 39.5°C and 40.5°C for 6 or 12 hours daily, from days 7 to 16 of embryonic development (ED), on hatchability, embryo mortality, hatching pattern, chick quality, yolk sac weight, breast muscle gene expression of Heat Shock Protein 70 (HSP70), Myogenic Differentiation 1 (MYOD), Type II Iodothyronine Deiodinase (DIO2), serum hormones and breast muscle histomorphometry at pulling. A total of 4,300 hatching eggs from a 39-week-old Ross 308 breeder flock were used. Eggs were randomly assigned to five treatments (860 eggs each) in a completely randomized design: a control treatment (37.5°C and 60% relative humidity (RH) until 18 ED) and four TM protocols applied daily: 39.5°C/6h, 39.5°C/12h, 40.5°C/6h, and 40.5°C/12h, all with 65% RH. The 40.5°C/12h treatment showed the lowest hatchability (31.55%) and Tona chick quality score (75.30) (P