Phytase and 1(alpha)-Hydroxycholecalciferol: Their Role in Improving Nutrient Bioavailability in Chickens and Pigs

Abstract

The mechanism by which hydroxylated vitamin D$\sb3$ compounds improve mineral utilization in chickens was evaluated using a variety of methodologies. In chicks fed vitamin D$\sb3$-adequate and P-deficient diets, supplemental 1$\alpha$-OH D$\sb3$ was unable to improve nonphytate-P utilization ($P<0.05$). In another assay, duodenal mucosal cells from chicks fed P-deficient diets, with or without supplemental 1$\alpha$-OH D$\sb3$, were obtained and analyzed for intestinal phytase activity. Chicks fed supplemental 1$\alpha$-OH D$\sb3$ had significantly higher bone ash values ($P0.10$) the specific activity of intestinal phytase in the duodenal mucosal tissue of chicks. Cecectomized chicks also were utilized to determine the role of microbially-produced phytase in the response to hydroxylated vitamin D$\sb3$ compounds. Bone ash responses to 1$\alpha$-OH D$\sb3$ and phytase supplementation were nearly identical in both cecectomized and sham-operated birds, indicating an insignificant role of the cecal microflora in the phytate-P releasing activity of 1$\alpha$-OH D$\sb3$. In conclusion, the marked phytate-P releasing capacity of dietary 1$\alpha$-OH D$\sb3$ and 1,25-(OH)$\sb2$ D$\sb3$ is apparently not caused by increased intestinal phytase activity.