Efficacy and phosphorus equivalency values of two bacterial phytases (Escherichia coli and Citrobacter braakii) allow the partial reduction of dicalcium phosphate added to the diets of broiler chickens from 1 to 21 days of age

The objective of this study was to determine the efficacy and the phosphorus equivalency of two bacterial phytases (Citrobacter braakii-derived phytase or genetically-modified Escherichia coli phytase) in the diets of broiler chickens from 1 to 21 days of age. A total of 2100 male broiler chickens were randomly distributed in 10 treatments with 10 replicates of 21 chicks each. A basal diet was formulated containing 1.8 g per kg of non-phytate phosphorus and 9 g per kg of total calcium (T1). For treatments 2–4, dicalcium phosphate was added to give 0.9, 1.8, or 2.7 g per kg of additional inorganic phosphorus. The treatments from 5 to 7 received 500, 1000, or 2000 phytase units of Citrobacter braakii (FYT) per kg while the treatments from 8 to 10 received 250, 500, or 1000 phytase units of Escherichia coli (FTU) per kg. Increasing levels of inorganic phosphorus from dicalcium phosphate at 0.9, 1.8, and 2.7 g per kg improved (P < 0.05) feed intake by 52, 71, and 80%; weight gain by 41, 75, and 32%; tibia ash weight by 64, 156, and 185%; and tibia phosphorus by 110, 323, and 378%, respectively. Increasing levels of Citrobacter braakii-derived phytase at 500, 1000, and 2000 FYT per kg contributed to a significant improvement (P < 0.05) of 52, 55, and 65% for feed intake; 37, 56, and 65% for weight gain; 52, 87, and 133% for tibia ash weight; and 96, 173, and 273% for tibia phosphorus, respectively. Increasing levels of Escherichia coli-derived phytase at 250 to 500, and 1000 FTU per kg increased (P < 0.05) feed intake by 50, 61, and 70%; weight gain by 49, 60, and 76%; tibia ash weight by 80, 103, and 164%; and tibia phosphorus by 128, 198, and 330%. Linear regression equations (P < 0.05) were used to estimate phosphorus equivalency values of the two phytases. The Citrobacter braakii- and Escherichia coli-derived phytases can be used in the diets of broiler chickens from 1 to 21 days of age to partially reduce the addition of dicalcium phosphate as a phosphorus source. The supplementation of 500, 1000, and 2000 phytase units of Citrobacter braakii per kg were determined to be equivalent to the average addition of 0.625, 1.091, and 2.024 g of inorganic phosphorus from dicalcium phosphate per kg in broiler diets, respectively. The supplementation of 250, 500, and 1000 phytase units of Escherichia coli per kg were determined to be equivalent to the average addition of 0.763, 1.307, and 2.395 g of inorganic phosphorus from dicalcium phosphate per kg in broiler diets, respectively.