METABOLISM AND NUTRITION The Effect of Different Levels of Nonphytate Phosphorus with and Without Phytase on the Performance of Four Strains of Laying Hens1

ABSTRACT A 4 × 7 factorial experiment was conducted to determine the effect of different nonphytate phospho-rus (NPP) regimens with and without phytase on perfor-mance of four strains of laying hens. The strains used were Babcock B300, DeKalb Delta White, Hy-Line W36, and ISA-White. The birds of T1 (Treatment 1), control diet, were fed a diet with 0.45 % NPP for the entire experi-ment (20 to 63 wk of age). The birds of T2 were fed a NPP regimen of 0.25 % for Phase 1 (20 to 35 wk of age), 0.2 % for Phase 2 (36 to 51 wk of age), and 0.15 % for Phase 3 (52 to 63 wk of age). The birds of T3 and T4 were fed a NPP regimen similar to T2 plus 150 or 300 units phytase/ kg diet, respectively. The birds of T5 were fed a NPP regimen of 0.2, 0.1, and 0.1 % for Phases 1, 2, and 3, respec-tively. The birds on T6 and T7 were fed a NPP regimen similar to T5, with 150 and 300 units phytase/kg diet, respectively. The criteria for evaluating the effect of di-etary treatments were production performance, shell quality, bone ash, and total P excretion. Production traits were drastically reduced and mortality was drastically increased when the birds of T5 were fed a diet with 0.1% NPP during Phase 2 (36 to 51 wk of age). Increasing the NPP level of this treatment from 0.1 to 0.45 % during Phase 3 restored the production traits almost to the control leve