To estimate the digestible lysine requirements for maintenance of roosters of different genotypes and body weight (Leghorn, ISA Label and Cobb 500), it was carried out three metabolic trials using the nitrogen balance (NB) technique. The birds were distributed in a completely randomized design with five levels of digestible lysine and six replications, and the experimental units consisted of one (trial 1) or two birds (trial 2 and 3). In each trial, the requirement of lysine for maintenance was obtained by linear regression of nitrogen balance (mg/kg0.75/day) by digestible lysine intake (mg/kg0.75/day), defined by the digestible lysine intake required to maintain nitrogen balance equal to zero. To compare the responses from the different genotypes, the nitrogen balance data obtained in the trials were analyzed by parallelism test, using the genotype as a classificatory variable and the digestible lysine intake as covariate. The requirement of digestible lysine did not vary among the genotypes, when it was established on the basis of metabolic weight, and was defined by the general equation: NB = _122.163 + 2.706 CLYS (P<0.001, r² = 0.67). Based on this equation, it was estimated the requirement of digestible lysine at 45.1 mg/kg0,75/day (32.3 mg/kg/day), regardless to the genotype. When they are established based on the content and degree of maturity of body protein, the lysine requirements are 173.6, 164.0 and 140.9 mg/PBm0.73.u/day for roosters Leghorn, ISA Label and Cobb 500, respectively.
amino acids; broiler chickens; factorial approach; nitrogen balance
