Estimated phosphorous requirement with and without added phytase of starting broiler chicks

Abstract

For poultry the availability of phosphorus from ingredients of plant origin is limited, because this element is bound to phytates, and birds do not produce the enzyme phytase. Thus, it is necessary to complement their diets with inorganic P. Recently, microbial phytase has been utilized to improve the availability of P from phytates. Two experiments were conducted to calculate the optimal biological level of available P (Pa) with and without phytase, and to evaluate the effect of phytase on body weight gain (WG) and ash content of the tibia (% ASH) of broilers from 1-21 days of age. In Expt. 1 seven levels of Pa were evaluate: 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, and 0.60%; in Expt. 2, four levels of Pa 0.15, 0.27, 0.39, and 0.51%, and four levels of phytase 0, 200, 400, and 600 FTU (units of phytase/kg of diet) were evaluated in a factorial arrangement. In Expt. 1 there were differences (P<.05) in WG and % ASH with the levels of 0.45 and 0.50% Pa being the best. The optimal biological level was 0.46% for WG, similar to the 0.45% proposed by NRC (1994); and 0.49% for%ASH. In Exp. 2 the effect of phytase level onWGand%ASH, followed a linear tendency, the 600 FTU level surpassing the 0 FTU level by 13.5% forWGand 8.5 for%ASH (P<.05). The optimal biological level (P<.05) of Pa forWGwas estimated as 0.47 with 0 FTU and 0.394% with 600 FTU, and for%ASH as 0.47% with 0 FTU and 0.43% with 600 FTU. For maximum WG it is possible to reduce the inorganic P level by 0.75 g/kg diet (0.075%) when supplementing with 600 FTU).