Determination and validation of available phosphorus equivalency of Escherichia coli-derived phytase in broiler diets

The objective of this experiment was to determine and validate the available phosphorus (AP) equivalency of Escherichia coli-derived phytase (ECP) in broiler diets. A total of nine hundred sixty 8-d-old broiler chicks were subjected to 8 dietary treatments with 10 replicates. The positive control (PC) diet contained recommended concentrations of calcium (Ca) and AP, whereas the negative control (NC) diet was formulated to contain 0.76% calcium and 0.10% AP. The remaining 6 diets included varying levels of AP from monosodium phosphate (MSP) or ECP. Nonlinear regression analysis indicated that AP equivalency values of 500 and 1,000 FTU/kg ECP were 0.986 and 1.589 g/kg, respectively. These values were validated in a subsequent growth trial. A total of two thousand 8-d-old broiler chicks were randomly allotted to 1 of 5 dietary treatments with 8 replicates. Five treatments included negative control diet 1 (NC1, highly deficient in AP and Ca), negative control diet 2 (NC2, deficient in AP and Ca), phytase diet 1 (P1, NC1 + 1,000 FTU/kg ECP), phytase diet 2 (P2, NC2 + 500 FTU/kg ECP), and positive control diet (PC, recommended concentrations of AP and Ca). Results indicated that birds fed diets supplemented with 500 or 1,000 FTU/kg ECP had similar growth performance and tibia characteristics compared with those fed PC diets. In conclusion, AP equivalency values of 0.986 and 1.589 g/kg AP determined for 500 and 1,000 FTU/kg ECP, respectively, can be applicable in commercial broiler diets.