EFFECTS OF 1,25-DIHYDROXYCHOLECALCIFEROL AND PHYTASE ON ZINC UTILIZATION IN BROILER CHICKS

Studies were conducted with com-soybean meal diets to evaluate the eff ects of phytate phosphorus utilization on zinc absorption and retentio n in broiler chicks. En the first two experiments, zinc-65 was used to determine zinc absorption. Experiment 1 was a 2 x 2 factorial with 0 or 5 mug/kg dihydroxycholecakiferol and 0 or 40 ppm supplemental zinc. In Experiment 2, 5 mug/kg 1,25-dihydroxycholecalciferol [1,25-(OH)2D3 ] or 750 units/kg phytase or both were added to a diet containing 35 p pm zinc. The diets in Experiment 3 were similar to Experiment 2 except that 600 units/kg phytase was fed. Experiment 4 was similar to Experi ment 3 except that dietary phosphorus was decreased by .15%. There wer e no treatment effects on body weight in Experiments 1 and 2. Zinc abs orption was higher in zinc-deficient birds in Experiment 1, but there were no other effects on zinc-65 absorption or retention. Body weight was increased by 1,25-(OH)2D3 in Experiments 3 and 4 and by phytase in Experiment 4. Phytate phosphorus retention was increased by phytase a nd 1,25-(OH)2D3 and was increased additively when both sources were fe d. Dietary 1,25-(OH)2D3 increased zinc retention at times during Exper iments 3 and 4, but this response was inconsistent. Phytase did not af fect zinc retention. Phytase plus 1,25-(OH)2D3 increased zinc retentio n synergistically in Experiment 3. Bone zinc was increased by 1,25-(OH )2D3 and phytase, and there was an additive effect in Experiment 3. Pl asma zinc and alkaline phosphatase were not affected. The results sugg est that supplemental zinc may be decreased in a com-soybean meal diet when phytate phosphorus utilization is enhanced.