Chronic Heat Exposure Enhances Fat Deposition and Modifies Muscle and Fat Partition in Broiler Carcasses

The effect of chronic heat exposure on carcass quality of broilers: proportion of lean and fat tissues, fat content, and fatty acid composition, was investigated. One hundred and eight 4-wk-old male chickens were brooded in individual battery cages in two controlled-environment rooms at constant ambient temperature (22 or 32 C) until 7 wk of age. They were equally distributed into three treatments: 22 C, ad libitum feeding (22AL); 32 C, ad libitum feeding (32AL); and 22 C, pair-feeding on the daily feed intake of heat-exposed chickens (22PF). At 7 wk of age, heat-exposed chickens (32AL) had a lower body weight gain than the other birds: -47% compared to 22AL and -31% compared to 22PF. At 32 C, broilers exhibited a lower breast to body weight proportion: 11.9 vs 13.4% for 22AL. Abdominal, subcutaneous, and intermuscular fat deposits were enhanced in hot conditions, respectively, 15, 21, and 22% compared to 22AL and 58, 64, and 33% compared to 22PF. However, lipid contents of abdominal, subcutaneous, intermuscular, and intramuscular tissues were not affected by heat exposure but were significantly reduced in the 22PF birds. In heat-exposed birds, although saturated fatty acid proportions, particularly palmitic acid (C16:0), were increased, unsaturated fatty acids as a percentage of total fatty acids were decreased, especially oleic (C18:1) and linoleic (C18:2) acids in fat tissues. Consequently, under ad libitum feeding conditions, heat exposure significantly decreased the unsaturated to saturated fatty acid ratio in the abdominal and subcutaneous fat tissues, but not in intermuscular and intramuscular fats.