Impact of Dietary Isoleucine Status on Heavy-Broiler Production

Abstract

Two experiments were conducted to evaluate the importance of Ile as a limiting amino acid in diets fed to broilers up to heavy market weights (35-54 d). The first experiment compared a control diet formulated to meet all critical limiting amino acids vs. a diet that also met all limiting amino acid needs except for Ile (0.71 vs. 0.58% standardized ileal digestibility). Results from Experiment 1 showed poorer BW gain, feed conversion and feed cost/BW gain in birds fed the Ile-marginal diet when compared to the control. Experiment 2 evaluated the supplementation of three graded levels of Ile (0.58, 0.62 and 0.66% standardized ileal digestibility) to the Ile-reduced diet used in Experiment 1. Results for Experiment 2 showed that BW gain and feed conversion improved when L-Ile was supplemented to the lowest dietary Ile level fed. Supplementation with equal amounts of Arg did not alleviate the dietary Ile limitation, thus validating the essentiality and marginality of Ile in practical corn-soybean meal diets when at least 2% of meat-and-bone meal is present in diet formulation.