LIMITING AMINO-ACIDS IN LOW PROTEIN MAIZE-SOYBEAN MEAL DIETS FED TO BROILER CHICKS FROM 3-WEEKS TO 7-WEEKS OF AGE

1. An experiment with separately housed male and female broiler chicks was carried out during the period of 3 to 7 weeks of age to determine the limiting amino acids (AA) in a low protein maize-soyabean meal diet. Chicks were fed on diets containing 170, 180, 190 and 200 g crude protein (CP)/kg with or without combined additions of L-threonine (Thr), L-tryptophan (Trp) and L-arginine (Arg) to those in the 180, 190 or 200 g CP/kg diets and a 170 g CP/kg diet with or without combined additions of Thr, Trp, Arg, L-isoleucine (Ile), L-leucine (Leu) and L-valine (Val) to those in the 190 g CP/kg diet. The diets were iso-energetic and contained the same concentrations of lysine (Lys) and sulphur-containing amino acids. 2. Decreasing the dietary CP had a significantly negative effect on performance. 3. No significant effects on performance were found when diets with 180 and 190 g CP/kg were supplemented with Thr, Trp and Arg to those in the 200 g CP/kg diet. 4. There were no significant differences in performance between the groups fed on the diets with 170, 180 and 190 g CP/kg when the 170 and 180 g CP/kg diets were supplemented with Thr, Trp and Arg to those in the 190 g CP/kg diet. 5. When 170 and 180 g CP/kg diets were supplemented with Thr, Trp and Arg to those in the 10 and 20 g/kg higher CP diets, male chicks showed a significantly positive effect only at the highest supplementation, while female chicks showed a significantly negative effect at both rates of addition. 6. It is concluded that Thr, Trp and Arg were limiting in diets with 170 g CP/kg, but only for male chicks from 6 to 7 weeks of age.