THREONINE REQUIREMENTS OF LAYING HENS

In order to determine the Thr requirement of laying hens, two experime nts were conducted using laying performance and plasma Thr concentrati on as parameters. At 29 and 39 wk Of age, 100 and 600 laying hens in E xperiments 1 and 2, respectively, with average BW and high egg product ion rate, were randomized, housed in individual cages, and given free access to water and experimental diets with five graded levels of Thr: 0.31, 0.39, 0.46, 0.54, and 0.61% for 21 d in Experiment 1 and diets with 0.31, 0.36, 0.41, 0.46 and 0.51% Thr for 58 d in Experiment 2. On the last day of the experiment, blood samples were taken for determin ation of plasma amino acid concentration. Feed intake and daily egg ma ss increased and then decreased linearly as dietary Thr increased. Pla sma Thr increased slowly, then sharply with increasing dietary Thr lev els. Using the broken-line model, the Thr requirements were estimated to be 0.425, 0.428, and 0.430% or 453, 456, and 458 mg/hen per d in Ex periment 1 and 0.395, 0.404, and 0.400%, or 457, 467, and 462 mg/hen p er d, in Experiment 2, for egg mass, feed efficiency, and plasma Thr c oncentration, respectively. These results indicate that the Thr requir ements expressed as milligrams per hen per day as determined by plasma Thr concentration agree with those of laying performance.