Additive effects of 1,25-dihydroxycholecalciferol and phytase on phytate phosphorus utilization and related parameters in broiler chickens.

Two experiments were conducted to compare the effects of supplementation with 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] and a commercial phytase on P utilization by broiler males. Experiment 1 was conducted with three levels of total dietary P (0.45,0.55, and 0.65%) in corn-soybean meal diets supplemented with 5 micrograms/kg of 1,25-(OH)2D3, 600 units/kg of phytase, or the combination of these supplements in a factorial arrangement from 0 to 21 d in battery brooders. A second experiment was conducted with a similar design except that it was carried out in floor pens for a period of 35 d. In Experiment 1, maximal BW was obtained at 0.65% P in chicks receiving the basal diet, 0.55% P in chicks receiving phytase or 1,25-(OH)2D3, and 0.45% P in chicks fed both supplements. Bone ash for chicks receiving the basal, phytase, 1,25-(OH)2D3, and combination treatments at 0.45% total dietary P were 26.6, 34.9, 35.1, and 38.8%. There were significant interactions between phytase and 1,25-(OH)2D3 for BW, bone ash, and incidence of rickets. Similar results were noticed in Experiment 2, with the exception that 1,25-(OH)2D3 had little influence on BW from 0 to 3 wk, likely due to slightly higher dietary P. From 3 to 5 wk, BW and bone ash were increased by each supplement and further increased by their combination. These interactions suggest different mechanisms of action for these supplements in influencing phytate P utilization.