Efficacy of a phytase derived from Escherichia coli and expressed in yeast on phosphorus utilization and bone mineralization in turkey poults.

A slope-response bioassay was conducted with male turkey poults to determine the sparing effect of P, based on improvements in bone mineralization in turkey poults, from 10 to 21 d of age when diets were supplemented with a novel phytase. Reference diets for calculation of the sparing effect of P contained 0.47, 0.55, 0.70, and 0.79% nonphytate phosphorus (NPP). Diets with varying dosages of a swine, Escherichia coli-derived AppA2 phytase (ECP) expressed in Pichia pastoris yeast (0, 250, 500, 750, and 1,000 U/kg) were added to the 0.47% NPP diet and improvements in bone mineralization determined the sparing effect of P supplied from ECP. Two additional reference diets were included that contained 500 U/kg from one of two commercial phytases (PA and PB) derived from Aspergillus and Peniophora. At 500 U/kg diet the ECP spared an additional 0.22% NPP (if calculated from tibia ash %), 0.18% NPP (if calculated from toe ash %), 0.24% NPP (if calculated from mg tibia ash), or 0.21% NPP (if calculated from mg toe ash). Phosphorus retention results validate bioassay results, in that 500 U ECP/kg resulted in 68.2% P being retained (0.49% of diet P retained) as compared with only 58.9% P being retained from the unsupplemented control diet (0.421% of diet P retained; P < 0.05).