Intestinal alkaline phosphatase and phytase of chicks: effect of dietary magnesium, calcium, phosphorus and thyroactive casein.

Abstract Broiler chicks (White Plymouth Rock and Vantress × W.P.R.) were raised to three weeks of age on a practical corn-soy ration. The experimental diets contained 0.2, 0.4 or 0.6% magnesium, 0.6, 1.0 or 1.5% calcium and 0.16, 0.48 or 0.80% inorganic phosphate. Thyroactive iodinated casein (1% thyroxine activity) was added to some diets at levels of 220–1760 p.p.m. The activities of alkaline β-glycerophosphatase and phytase (inositolhexaphosphate phosphohydrolase) were determined in homogenates of duodenal mucosa after three weeks on each dietary regimen. High dietary levels of magnesium and calcium were found to reduce the activity of both enzymes, while high levels of phosphate had no effect. The lowest level of dietary phosphate greatly increased the activities of alkaline phosphatase and phytase. Thyroactive casein feeding increased the activity of both phosphatases, especially the calcium-depressed enzymes. Both enzyme activities were very much higher in the Vantress × W.P.R. chicks than in the parent (White Plymouth Rock) strain, but the former birds were less affected by thyrocasein. Phytase activity was affected by the same factors as alkaline phosphatase, but to a greater degree in each case.