Live performance and environmental impact of broiler chickens fed diets varying in amino acids and phytase

This research examined the effects of decreasing dietary amino acid density (AAD) and potential interactions of AAD and phytase on growth and nitrogen (N) and phosphorus (P) excretion of broiler chickens. In experiment 1, diets were formulated to high (H) or moderate (M) AAD during prestarter (1-7 days), starter (8-19 days), and grower (20-35 days) resulting in the following dietary treatments: HHH, HHM, HMM, and MMM. The HHH feeding regimen improved (P <= 0.05) body weight gain (BWG) and feed conversion (FCR) from I to 35 days of age, but increased (P <= 0.05) N content of the excreta by 180 g/kg. In Experiment 2, three diets were fed from 36 to 49 days varying in AAD (H, M, and low, L) with (500 units/kg) or without supplemental phytase. Broilers fed a diet formulated to L AAD had high FCR. Increasing AAD increased (P <= 0.05) N excretion by 0.56 and 0.80 g per bird compared with M and L AAD, respectively. Phytase supplementation reduced (P <= 0.05) P excretion by 0.18 g per bird, but BWG and FCR were not affected. Dietary phytase and AAD did not interact to reduce N excretion. These results indicate that N excretion could be reduced with dietary manipulation, but effects on FCR should be considered. Published by Elsevier B.V.