Digestible lysine concentrations and amino acid densities influence growth performance and carcass traits in broiler chickens from 14 to 35 days post-hatch

Abstract

The present study was conducted to evaluate the responses of growth performance and carcass traits in Cobb MV × 500 fast feathering broiler chickens fed maize, soybean meal (SBM) and peanut meal based diets containing different levels of digestible (dig) lysine (Lys). Dietary treatments consisted of 6 concentrations of dig Lys that ranged from 8.4 to 12.9 g/kg in increments of 0.9 g/kg. Two control diets with the medium level of dig Lys concentration of 11.1 g/kg were included where the positive control (PC) diet was a typical commercial diet based on maize and SBM and the negative control (NC) diet replaced part of SBM with100 g/kg peanut meal to allow higher supplementations of feed grade amino acids. Each of the eight experimental diets were offered to either male or female broiler chickens to form 16 experimental treatments and each treatment included 6 floor pens with 12 birds per pen. Broiler chickens were offered experimental diets from 14 to 35 days post-hatch. All diets were balanced with essential amino acids (EAA) by using ideal protein ratio approach and were offered to broiler chickens from 14 to 35 days post-hatch. Predictably, male broiler chickens had better weight gain (WG), feed intake (FI), feed conversion ratio (FCR) and breast meat yield (P < 0.001) than female birds. Sex did not influence yield of wings (P = 0.174) and thighs (P = 0.243). There were no interactions between sex and dietary dig Lys levels on growth performance and linear improvements were observed for live body weight (BW), WG and FCR. By comparing three mathematical models, in female birds, the dig Lys requirement was estimated at 11.5 g/kg for optimal WG and 12.1 g/kg for FCR. In male broiler chickens, the dig Lys requirement was estimated at 10.3 g/kg for optimal WG and 12.2 g/kg for FCR. The results suggested that modern broilers are highly responsive to dietary amino acid (AA) density and regular evaluations of AA requirements are needed because of genetic progress of modern broiler chickens.