Two trials wereconducted to evaluate the requirements of increasing dietary digestible lysinelevels, maintaining or not the amino acids relation, for broilers from 1 to21 days old, on thermoneutral environment. A complete randomized experimentaldesign was used in both trials. In trial 1, broilers were allotted to five treatments(0.92, 0.98, 1.04, 1.10, and 1.16% digestible lysine levels, conventional diet),with eight replicates of ten birds. In trial 2, chicks were allotted to fourtreatments (1.04, 1.10, 1.16, and 1.22% of digestible lysine, in diets maintainingamino acid relation) with eight replicates of ten birds. In trial 1, effectsof dietary lysine levels on body weight gain and feed intake, both increasingquadraticly up to 1.13 and 1.11% digestible lysine, respectively, were observed.There was significant treatment effect on feed:gain ratio, that decreased quadraticlyup to 1.14% digestible lysine. Absolute carcass weight increased quadractilywhile relative carcass values and absolute weight of gizzard increased linearlywith treatments. Relative weights of heart and intestines decreased linearlywith the treatments. In trial 2, body weight gain also increased linearly withtreatments, the LRP model better adjusted to data, where the 1.17% digestiblelysine level was estimated. No effects of treatments on feed intake and feed:gainratio were detected. Absolute carcass weight was linearly affected by the increasingdietary lysine levels. There was no effect of dietary lysine levels on absoluteand relative weights of all evaluated organs. It was concluded that Avian Farmsmale broilers, in the period from 1 to 21 days, require at least 1.14 and 1.17%digestible lysine, in a conventional diet or of a diet maintaining the aminoacid relation, respectively, on a thermoneutral environment.
