Nutritional requirement of digestible threonine for white egg layers of 60 to 76 weeks of age

The objective of this study was to determine the requirement for digestible Thr for optimum performance of white egg layers in the period from 60 to 76 wk of age. DeKalb White Leghorn layers with an average weight of 1,345 kg were distributed 5 increasing levels of digestible Thr (0.523, 0.546, 0.569, 0.592, and 0.615%) in a completely randomized design, with 6 replicates and 6 birds per experimental unit for a total of 180 birds. The dietary treatments contained 0.759% of digestible Lys, which was obtained using the prediction equation of the Brazilian Tables for Poultry and Swine, and each treatment consisted of a digestible Thr-to-Lys ratio of 69, 72, 75, 78, or 81%. The digestible Thr levels had a linear effect on feed intake and a quadratic effect on egg production, egg mass, and feed conversion per mass and per dozen eggs. In conclusion, a digestible Thr-to-Lys ratio of 75.14% is recommended for White Leghorn of 60 to 76 wk of age, corresponding to the level of 0.570% in the diet and a daily intake of digestible Thr of 622 mg/bird.