Performance and Carcass Composition of Broilers under Heat Stress : II. The Effects of Dietary Lysine

An experiment was conducted to determine the effect of lysine on performance and carcass composition of broilers under heat stress during the grower period (3-6 weeks). A factorial arrangement of three levels of dietary protein (18, 20, and 22%), three levels of dietary lysine (1.26, 1.39, and 1.52%), and two rearing temperature regimens were used in this study. Birds were kept under either moderate temperature ($24{\pm}1^{\circ}C/24h$) or hot cycling temperature ($26-34^{\circ}C/6h$, $34{\pm}1^{\circ}C/12h$, and $34-26^{\circ}C/6h$). Body weight (BW), weight gain (WG), feed intake (FI), feed conversion (FE), carcass weight (CW), carcass yield (CY), and percentages of breast meat (BM), abdominal fat (AF), drumsticks (DS), and thighs (TH) were determined at the end of experiment. Exposure to high ambient temperature significantly (p<0.05) decreased BW, WG, FI, FE, CW, BM, AF, and increased CY, DS, and TH. High dietary protein significantly (p<0.05) decreased AF and TH, and improved CW only under moderate temperature, resulting in significant (p<0.05) protein by temperature interaction. High dietary lysine significantly (p<0.05) decreased BW, WG, FI, CW, CY and AF, while BM was reduced only when high dietary protein was fed, resulting in significant (p<0.05) protein by lysine interaction. It is concluded that increasing dietary lysine adversely affected broilers' performance and carcass composition irrespective of rearing temperature.