Optimum standardized ileal digestible tryptophan intake for broiler chickens

Abstract

Six feeding trials were conducted to determine the optimum intake of standardized ileal digestible (SID) tryptophan of male and female broiler chickens in the starter (0 to 14 d), grower (14 to 28 d), and finisher (28 to 42 d) phases. In each trial, 640 broiler chickens were randomly assigned to 1 of 8 treatments, with 4 replicates of 20 broiler chickens. Diets were formulated by mixing a high and a low protein diet in different proportions, and dietary concentrations of SID Trp ranged 0.56 to 2.94, 0.54 to 2.75, and 0.52 to 2.60 g/kg in the starter, grower, and finisher phases, respectively. Tryptophan intake was regressed against average daily gain (ADG) and feed conversion ratio (FCR) using polynomial regression and broken-line regression model and the model that better fitted data was chosen according to Bayesian information criterion. Broiler chickens responded quadratically to increasing dietary Trp concentration and ADG was maximized at 86, 264, and 441 mg SID Trp/d for male broiler chickens (R2 = 0.96; P < 0.01) and at 76.5, 237, and 278 mg SID Trp/d for females (R2 = 0.97; P < 0.01) in the starter, grower and finisher phases, respectively. Feed conversion ratio was optimized at 69.9, 247, and 338 mg SID Trp/d for males (R2 = 0.91; P < 0.01) and 67.8, 223, and 280 mg SID Trp/d for females (R2 = 0.93; P < 0.01) in the starter, grower, and finisher phases, respectively. The optimum SID Trp intake for each sex and phase was determined based on ADG.