THE EFFECTS OF SUPPLEMENTAL MICROBIAL PHYTASE ON THE PERFORMANCE AND UTILIZATION OF DIETARY CALCIUM, PHOSPHORUS, COPPER, AND ZINC IN BROILER-CHICKENS FED CORN-SOYBEAN DIETS

A 3-wk feeding trial with 180 sexed day-old broiler chickens was condu cted to study the efficacy of microbial phytase (Natuphos 1000) on gro wth performance, relative retention of P, Ca, Cu, and Zn, and mineral contents of plasma and bone. Treatments involved a normal P level corn -soybean diet, a low-P diet, and a low-P plus phytase (600 phytase uni ts/kg) diet. Phytase supplementation increased (P less than or equal t o 0.05) body weight in male and female chickens by 13.2 and 5.8%, resp ectively, at 21 d. The improvements yielded body weights comparable to those obtained on the normal P diet. Phytase supplementation overcame (P less than or equal to 0.05) the depression of feed intake observed on the low-P diet. Treatments had no effect on feed:gain ratio. Phyta se supplementation of the low-P diet increased (P less than or equal t o 0.05) the relative retention of total P, Ca, Cu, and Zn by 12.5, 12. 2, 19.3, and 62.3 percentage units, respectively, in male chickens. Mi crobial phytase increased the plasma P by 15.7% and reduced (P less th an or equal to 0.05) the Ca concentration by 34.1%, but had no effect on plasma concentrations of Cu or Zn. Phytase supplementation increase d the percentage ash in both head and shaft portions of dry, fat-free tibia bone to a level comparable to that of the normal-P diet. Phytase supplementation had no effect on the concentration of any of the mine rals measured in whole tibia ash but did increase (P less than or equa l to 0.05) the DM percentage of P and Ca in tibia head of male chicken s by 0.65 and 1.4 percentage units, respectively. These results show t hat microbial phytase supplementation of a low-P diet increased growth and relative retention of total P, Ca, Cu, and Zn and improved bone m ineralization in broiler chickens.