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 supplementati on with 1,25-dihydroxycholecalciferol [1,25-(OH)(2)D-3] and a commerci al phytase on P utilization by broiler males. Experiment 1 was conduct ed with three levels of total dietary P (0.45, 0.55, and 0.65%) in cor n-soybean meal diets supplemented with 5 mu g/kg of 1,25-(OH)(2)D-3, 6 00 units/kg of phytase, or the combination of these supplements in a f actorial arrangement from 0 to 21 d in battery brooders. A second expe riment 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 wa s obtained at 0.65% P in chicks receiving the basal diet, 0.55% P in c hicks receiving phytase or 1,25-(OH)(2)D-3, and 0.45% P in chicks fed both supplements. Bone ash for chicks receiving the basal, phytase, 1, 25-(OH)(2)D-3, and combination treatments at 0.45% total dietary P wer e 26.6, 34.9, 35.1, and 38.8%. There were significant interactions bet ween phytase and 1,25-(OH)(2)D-3 for BW, bone ash, and incidence of ri ckets. Similar results were noticed in Experiment 2, with the exceptio n that 1,25-(OH)(2)D-3 had little influence on BW from 0 to 3 wk, like ly due to slightly higher dietary P. From 3 to 5 wk, BW and bone ash w ere increased by each supplement and further increased by their combin ation. These interactions suggest different mechanisms of action for t hese supplements in influencing phytate P utilization.