THE EFFECT OF DIETARY PHYTASE ON GROWTH-PERFORMANCE AND PHOSPHORUS UTILIZATION OF BROILER CHICKS

Two experiments were conducted to evaluate the effect of dietary phyta se and increasing levels of available phosphorus (P(av)) on the growth performance and phosphorus metabolism of broiler chicks. In both expe riments, graded levels of P provided by dicalcium phosphate and of phy tase were added to a low-P com-soybean meal basal diet. In Experiment 1, diets providing .21, .29, .37, and .44% P(av) without phytase; .21% P(av) plus .05, .10, or.30% phytase; and.29% P(av) plus .10% phytase were each fed to four groups of seven chicks, 3 days of age. In Experi ment 2, diets providing P(av) levels of .32, .38, and.44% and phytase levels of.5, 1.0, and 1.5% (250,500, and 750 units/kg) in a factorial arrangement were each fed to four groups of eight chicks, 5 days of ag e. In Experiment 1, increasing dietary P(av), but not phytase, increas ed feed intake, weight gain, feed conversion, plasma inorganic P, tibi a and toe ash, and tibia breaking strength (P less-than-or-equal-to .0 5). Plasma inorganic P responded quadratically to increasing dietary p hytase. In Experiment 2, feed intake and weight gain were increased by elevating the level of P(av), but not by phytase. Toe and tibia ash a nd plasma inorganic P were increased by dietary phytase and increasing levels of P(av) (P less-than-or-equal-to .01). Tibia breaking strengt h was improved (P less-than-or-equal-to .05) by dietary phytase but no t by increasing levels of P(av). The P excretion was elevated (P less- than-or-equal-to .01) by increasing levels of P(av) and was decreased by supplemental phytase (P less-than-or-equal-to .05). Dietary phytase added to diets low in P(av) was able to improve some, but not all var iables studied.