The objective of this work was to determine, through a digestibility assay, the nutritional requirement of true digestible lysine for broiler chickens, in the four growing phases. Four performance experiments, previously performed, allowed the determination of total lysine requirement of broiler chickens in the periods from 1 to 21, 15 to 40, 22 to 40 and 42 to 48 days of age. Thirty cecectomized adults Leghorn roosters were used, with an average weight of 2316±190 g, and individually caged in batteries with excreta collecting trays and using the precision feeding method. A completely randomized design was used, with five treatments (four with diets and one fasted) and six replications. The basal diets from the four growing phases, contained 1.0, 0.825, 0.80 and 0.75% total lysine, were used. Based on the determined digestibility coefficients of 93.3; 93.58; 89.76 and 92,25% and considering the supplemented L-Lysine HCL as 100 % digestible, the true digestible lysine requirements were: 1.130%; 1.075%; 0,95% and 0,84% for 1-21; 15- 40; 22-40 and 42-48 days of age, respectively. Using the linear regression model, the obtained equations were <img src="http:/img/fbpe/rbz/v29n4/5608s1.gif">(%total lysine/Mcal) = 0.4335 - 0,003284X R² 0.98 and <img src="http:/img/fbpe/rbz/v29n4/5608s1.gif">(% digestible lysine/Mcal) = 0,41081 - 0,003213X, R² 0.96 for total and digestible lysine, respectively, where x was the average birds age in days.
broiler; digestible lysine; nutritional requirement; rooster
