Effect of different timing of exposure to heat and strains on the carcass yield and breast chemical composition of broiler

The effects of different exposure periods under heat on the carcass yield, cuts and edible organs and breast chemical composition of broilers from two strains were investigated. Five hundred and sixty Cobb 500 Slow (R) and 560 Hubbard Flex (R) broiler chicks were housed in 32 pens and from the 14th day on, they were divided in thermal environments: control, 1 hour, 2 hours or 3 hours a day under heat stress. Carcass yield, boneless breast, thigh and drumstick with bone, wings, feet, liver, gizzard and heart were evaluated in six birds of each strain in each thermal environment. Samples were obtained to assess dry matter, ether extract, crude protein and mineral matter. The cyclic heat stress for up to three hours a day did not influence 33 the carcass yield, boneless breast, thigh and drumstick, wing, heart, gizzard, liver, and the breast chemical composition. Cobb 500 Slow (R) strain had higher breast yield. Hubbard Flex (R) had breast with higher percentage of mineral matter and protein. Cobb strain is best designed to breast production, and Hubbard is best for whole chicken production.