This paper was developed to evaluate the performance and the carcass characteristics of broiler chickens over the period from 22 to 42 days, fed with diets formulated with different digestible lysine: crude protein (CP) ratio. A completely randomized experimental design was used, according to a model with two criteria of hierarchical rank. A total of 1,200 male broiler chicks of the Cobb strain, raised upy to 21 days of age, when the birds were uniformized with average weight of 879 ± 17 g and distributed into the experimental plots. The diets were isonutrient, except for the levels of CP and digestible lysine, formulated with two levels of CP 17.0 and 19.5%, and five digestible lysine : CP ratios, corresponding to 5.9; 6.4; 6.9; 7.4 and 7.9% within the diet of 17.0% CP and 5.3; 5.7; 6.1; 6.5 and 6.9% on the diet with 19.5% CP. Each experimental diet was supplied to 20 birds in each one of the six replicates. At 42 days, the performance characteristics (weight gain, feed consumption and feed conversion) were evaluated, and two birds from each plot were slaughtered for determination of carcass yield, cuts and abdominal fat. Feed consumption was reduced feed conversion improved linearly according to the ratios evaluated within the level of 17.0% CP. There was no significant effect of the two levels of CP used, on weight gain, characteristic carcass and cuts yield. Abdominal fat linearly reduced in the level of 19.5% CP. The ideal ratio was of 5.9% for 17.0% CP and 5.3% for 19.5% CP. The CP level of the diet can be reduced for 17.0%, with no effect on bird performance.
birds; digestible amino acids; ideal protein; requirement
