Embryonic thermal manipulation and dietary fat source during acute heat stress: 2. Effect on broiler carcass characteristics and breast muscle myopathies

SUMMARY: The objective of this study was to evaluate the effect of embryonic thermal manipulation and dietary fat source during the finisher period on carcass characteristics and breast muscle myopathies following acute heat stress. Thermal manipulation (TM) of incubation temperatures has been shown to improve bird resistance to heat stress and enhance breast muscle growth. Fat supplementation is frequently used during heat stress and fat source may alter carcass composition, as fat sources rich in unsaturated fatty acids have been shown to reduce fat pad weight. Ross 708 eggs were incubated at 37.5°C except during TM when temperature was increased to 39.5°C for 12 h daily from embryo day 7 to 16. A total of 1,080 chicks were reared under standard conditions until acute heat stress at 43 d. Dietary treatments were applied during the finisher period beginning at 28 d, with diets including 4.5% of soya oil, poultry fat, or olive oil. At 49 d, 240 male birds were processed to assess carcass and portion weights, as well as breast quality. Carcass and portion weights were decreased by TM, however percent yield was similar to the controls. A decrease in breast muscle myopathies was noted but may have been due to the lower BW of the TM birds. Interactions between the treatments suggest that TM may alter lipid metabolism. Differences in dietary fat source did not affect carcass characteristics. The reduction in breast muscle myopathies may be negated by the negative impact of TM on carcass weights.