With the objective to establish the nutritional requirement of threonine for light and semi-heavy laying hens in the period from 34 to 50 weeks old, 580 laying hens (half Lohmann and half Lohmann Brown) submitted to a basal ration containing 2.850 kcal ME/kg, 14.0% CP, supplemented of five levels (0.00, 0.035, 0.07, 0.105, and 0.140%) of L-threonine, in order to provide 0.410, 0.445, 0.480, 0.515, and 0.550% of digestible threonine in the rations. A 5 x 2 (threonine level and laying hen strain) factorial arrangement, with six replications per treatment and six hens per experimental unit in a completely randomized design was used. Egg production (%), egg mass and average egg weight (g), feed intake (g/hen.day), feed conversion (kg feed/egg dozen), body weight change (g) and internal egg quality (Haugh Units, albumen and yolk index) were evaluated. The threonine levels did not affect the body weight change, feed intake, egg weight and internal egg quality in both laying hen strains. Feed conversion, egg production, egg mass and Haugh units were positive influenced by the threonine level. The digestible threonine requirement, estimated by the quadratic model, for the light and the semi-heavy laying hens, was 0.510 and 0.517% in the diet, corresponding to the daily intake per hen of 583 and 575 mg lysine/day, respectively.
digestible amino acid; ideal protein; layer; poultry
