Ideal amino acid profile and dietary lysine specification for broiler chickens of 20 to 40 days of age

1. The aim of the study was to determine the ideal ratio of the essential a mino acids lysine (Lys), methionine (Met), threonine (Thr), tryptophan (Trp ), arginine (Arg), valine (Val) and isoleucine (Ile) and to assess the requ ired dietary lysine concentration for optimum performance in broiler chicke ns of 2 commercial strains from 20 to 40 d of age. 2. An identical basal diet was used throughout all experiments. It consiste d mainly of maize and soyabean meal and contained 172 g crude protein and 1 3.2 MJ AME(N) per kg. For each experiment, the basal diet was adequately su pplemented with all essential amino acids except the one to be tested, whic h was supplemented in 6 graded concentrations in exchange for maize starch. One (Met, Trp, Arg, Val, Ile) or 2 (Lys, Thr) growth trials were conducted per amino acid tested and the response in weight gain, food: gain ratio, b reast meat yield and abdominal fat were examined. 3. The ideal amino acid ratio relative to Lys (expressed as a percentage) w as calculated to be 75% Met+Cys, 63% Thr, 19% Trp, 112% Arg, 71% Ile and 81 % Tial on a true faecal digestible basis when the data were subjected to br oken-line regression analysis. From both lysine studies the concentration f or optimum food: gain ratio was calculated, by exponential regression analy sis, to be 11.5 g true faecal digestible lys per kg diet.