A study was conducted to evaluate the separate response to Lysine (Lys) and to Methionine (Met) in diets on live performance of young broiler chickens from 0 to 18 d of age. Corn and soybean meal of known protein and moisture content were used to formulate basal diets to provide 0.90 to 1.40% digestible Lys in increments of 0.10%. The mean of suggested amino acid ratios to Lys suggested by literature values was used in formulation according to the ideal protein concept. All amino acids other than Met and TSAA were calculated to meet or exceed the expected ratio to Lys. Diets were calculated to be isocaloric with 3086 kcal/kg ME and were supplemented with inorganic trace mineral premix to avoid any source of Met from this premix. Experimental diets were prepared by addition of variable amounts of MHA (84% of Met) and cornstarch to the Lys basal diets to provide increments of 0.04% up to 0.28% supplemental Met activity for each level of digestible Lys, with a 6 × 8 factorial arrangement of 6 levels of Lys and 8 levels of supplemental Met resulting in a total of 48 treatments. Each of the 48 experimental diets was fed to 6 replicate pens of 6 male chicks (Cobb500). Body weights by pen were obtained at 1 and 18 d of age with feed consumption determined during the test period. The ANOVA considered levels of Lys and Met and their interaction. There was significant (P < 0.05) effect of the dietary Lys level on feed intake, body weight gain and feed conversion ratio, with optimal level close to 1.2% of digestible Lys for both body weight gain and feed conversion ratio. There was no significant (P < 0.05) effect of the added Met level on feed intake, body weight and feed conversion ratio, indicating that the Met level in the basal diet of this study might be sufficient to support body weight and feed conversion ratio. No significant interactions were observed between Lys and Met for these 3 parameters. Results of this study suggest that the response to variation in Lys is a
