Effects of 1,25-Dihydroxycholecalciferol and Phytase on Zinc Utilization in Broiler Chicks1

ABSTRACT Studies were conducted with corn-soybean meal diets to evalu-ate the effects of phytate phosphorus utilization on zinc absorption and retention in broiler chicks. In the first two experiments, zinc-65 was used to determine zinc absorption. Experiment 1 was a 2 x 2 factorial with 0 or 5 /ig/kg dihydroxycholecalciferol and 0 or 40 ppm supplemental zinc. In Experiment 2, 5 ng/kg 1,25-dihydroxycholecalciferol [l,25-(OH)2D3] or 750 units/kg phytase or both were added to a diet containing 35 ppm zinc. The diets in Experiment 3 were similar to Experiment 2 except that 600 units/kg phytase was fed. Experiment 4 was similar to Experiment 3 except that dietary phosphorus was decreased by.15%. There were no treatment effects on body weight in Experiments 1 and 2. Zinc absorption 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 l,25-(OH)2D3 in Experiments 3 and 4 and by phytase in Experiment 4. Phytate phosphorus retention was increased by phytase and l,25-(OH)2D3 and was increased additively when both sources were fed. Dietary l,25-(OH)2D3 increased zinc retention at times during Experiments 3 and 4, but this response was inconsistent. Phytase did not affect zinc retention. Phytase plus l,25-(OH)2D3 increased zinc retention synergisti-cally in Experiment 3. Bone zinc was increased by l,25-(OH)2D3 and phytase, and there was an additive effect in Experiment 3. Plasma zinc and alkaline phosphatase were not affected. The results suggest that supplemental zinc may be decreased in a corn-soybean meal diet when phytate phosphorus utilization is enhanced. (Key words: 1,25-dihydroxycholecalciferol, phytase, phytate phosphorus, tibial dyschondroplasia, zinc