Amino Acid Density and L-Threonine Responses in Ross Broilers1,2

Abstract: An experiment was conducted to determine the effects of feeding broilers diets differing in amino acid density during the finisher period. Also, the impact of L-threonine addition to high (H) or low (L) amino acid density diets was determined. Ross x 708 male broiler chicks were placed in floor pens and fed common diets from d 1 to 34 that met or exceeded NRC (1994) recommendations. From d 35 to 55, broilers were fed diets consisting of H (digestible Lys of 0.88%, TSAA of 0.69%, and Thr of 0.59%) or L (digestible Lys of 0.82%, TSAA of 0.64%, and Thr of 0.55%) amino acid density, with or without dietary L-threonine (9 replications each of 4 treatments). On d 55, live performance and carcass characteristics were determined. There were no interactions or L-threonine effects (P>0.05) on live performance or carcass traits of broilers. Body weight and feed intake did not differ due to amino acid density. Birds fed diets containing H amino acid density had higher (P< 0.05) breast meat yield (P = 0.06 relative to BW; P = 0.01 relative to carcass weight) and lower (P<0.05) feed conversion and percentage abdominal fat than birds fed diets with L amino acid density. Minimizing essential amino acid excesses through dietary L-threonine inclusion did not improve or adversely affect performance. An economic analysis indicated that decreasing amino acid density (H to L) in 35 to 55 d broilers resulted in an income loss of $0.10/live bird