Phosphorus equivalency value of an Escherichia coli phytase in the diets of White Pekin ducks

Male White Pekin ducks at 7 d posthatch were used in a 10-d experiment to determine the equivalency value of an Escherichia coli phytase (Phyzyme XP) in corn-soybean meal-based mash diets. Two hundred fifty-six ducks were grouped by weight into 8 blocks of 8 cages with 4 ducks per cage. The 8 diets consisted of a P-adequate positive control corn-soybean meal formulated to contain CP, Ca, total P, and non-phytate P at 220, 8, 6.6, and 4 g/kg, respectively; a low-P negative control (NC) corn-soybean meal basal diet formulated to contain CP, Ca, total P, and non-phytate P at 220, 6.5, 3.9, and 1.3 g/kg, respectively; NC diet plus 0.5, 1.0, or 1.5 g of inorganic P from monosodium phosphate/kg; and NC diet plus E. coli phytase at 500, 1,000, or 1,500 units/kg. Ducks were provided ad libitum access to water and experimental diets. Feeding the low-P NC diet to ducks reduced (P < 0.01) BW gain, feed intake, G: F, tibia ash, ileal digestibility, and utilization of P. Supplementation of the NC diet with inorganic P or phytase linearly improved (P < 0.01) final weight, BW gain, feed intake, G: F, tibia ash, and ileal P digestibility. There were linear increases (P < 0.01) in the utilization of P from 33.8 to 42% or from 33.8 to 46.6% as dietary added inorganic P or phytase increased from 0 to 1.5 g/kg or 0 to 1,500 units/kg, respectively. Linear regression equations for the tibia ash as the dependent variable and supplemental intake of inorganic P and phytase or supplemental level of inorganic P and phytase as independent variables were used to generate P equivalency values of phytase. The mean P equivalency values of phytase from linear regression equations derived from ducks fed a low-P NC diet supplemented with graded levels of inorganic P or phytase from d 7 to 17 posthatch for 500, 1,000, and 1,500 phytase units/kg of diet were 0.453, 0.847, and 1.242 g/kg of diet, respectively. The results of this study showed that this phytase was efficacious in hydrolyzing phytate P for bone mineralization and growth of ducks.