EFFICACY OF SUPPLEMENTAL MICROBIAL PHYTASE AT DIFFERENT DIETARY CALCIUM LEVELS ON GROWTH-PERFORMANCE AND MINERAL UTILIZATION OF BROILER-CHICKENS

A 3-wk feeding trial with 240 sexed, day-old broiler chickens was cond ucted to determine the efficacy of microbial phytase at different leve ls of dietary Ca on performance and utilization of minerals in broiler chickens fed a low-P corn-soybean diet. The experimental design was a 3 x 2 factorial arrangement of treatments; Ca at 0.6, 1.0, and 1.25% and phytase at 0 and 600 phytase U/kg diet. Phytase supplementation, r egardless of Ca level, increased (P less than or equal to 0.005) feed intake, (P less than or equal to 0.0001) body weight, and (P less than or equal to 0.025) feed efficiency at 21 d; the optimum levels of bod y weight, feed intake, and feed efficiency were obtained with low (0.6 %) dietary Ca plus phytase. Retentions of P, Ca, and N were increased (P less than or equal to 0.05) by phytase supplementation. Although th e maximum retentions of P and N were obtained at the 1.0 and 1.25% Ca levels, respectively, they were not significantly different from the v alues obtained at 0.6% Ca. The increasing level of dietary Ca decrease d plasma P (P less than or equal to 0.05) and Cu (P less than or equal to 0.06). Phytase supplementation had the opposite effect; i.e., incr eased plasma P (P less than or equal to 0.03) and Cu (P less than or e qual to 0.02). The maximum level of plasma P was obtained with phytase at the 1.0% Ca level, but this value was not significantly different from the value obtained with phytase at the 0.6% Ca level. Phytase sup plementation increased (P less than or equal to 0.04) the ash content of both tibia head and shaft but had no effect on mineral contents in the ash. The optimum level of ash content was observed with the 0.6% C a diet plus phytase. The results show that microbial phytase supplemen tation to a low P diet improved growth performance and mineral utiliza tion in broiler chickens. Dietary Ca levels had a significant effect o n the response to phytase; the optimum growth performance and mineral utilization were achieved at the low (0.6%) level of dietary Ca supple mented with phytase.