Effect of digestible threonine on performance, egg quality, blood metabolites, and immune responses in laying hens fed a wheat-based diet in the second cycle.

The current experiment was conducted to evaluate the effects of digestible threonine (dThr) on performance, egg quality, blood metabolites, and immune responses in laying hens fed a wheat-based diet during the second cycle. Also, dThr requirements were determined based on nutrient dose-response data. A total of 384, 105-week-old post-molt Hy-line-W36 laying hens were allocated to six groups, 0.02% increments, ranging from 0.44 to 0.54% dThr, with eight replicates/treatment and eight birds each, from 105 to 116 wk. By increasing, dThr levels improved egg weight with a linear trend (p <.01), and egg production (EP), egg mass (EM), and feed conversion ratio (FCR) with quadratic trends (p <.05). Hens fed diet contained 0.48% dThr, dThr/digestible Lys (dLys) of 66% showed the best egg production traits. However, feed intake, egg quality traits, blood metabolites, and immune responses were unaffected by dThr levels. Based on the quadratic broken‐line regression models, the dThr requirements of laying hens during the second production cycle for optimised the EP, EM, and FCR were estimated at 507, 514, and 520 mg/hen per day, respectively. These values correspond to 9.84–10.1 mg/g of EM. It is concluded, in the laying hens fed a wheat-based diet during the second cycle, the dietary dThr level of 0.48%, dThr/dLys of 66%, and a daily intake of 520 mg dThr/bird are adequate for optimised performance. The amino acids requirements of laying hens vary depending on trait is considered for optimisation. The dThr requirement estimated for FCR was higher than those for EP and EM. In the laying hens that feed a wheat-based diet during the second cycle. A dietary digestible threonine concentration of 0.48% and a daily intake of digestible threonine 520 mg/bird are adequate for optimised performance. [ABSTRACT FROM AUTHOR]