Influence of Supplemental 25-hydroxy- Cholecalciferol and Phytase on Production Performance of Laying Hens Fed Diets Low in Phosphorus

s of papers 11 42 Phosphorus efficacy of an E. coli phytase in young chicks. N.R. Augspurger*1, D.M. Webel2, X.G. Lei3, and D.H. Baker1, 1University of Illinois at Urbana-Champaign, 2United Feeds, Inc., Sheridan, IN, 3Cornell University, Ithaca, NY. Three assays were done to investigate the phosphorus (Pi)-releasing efficacy of an E. coli phytase (ECP, produced by Phytex LLC), relative to Natuphos r (BASF Corp.), when added to P-deficient corn-soybean meal diets. Natuphos r initiates its attack on phytate at the 3 position, whereas ECP begins at the 6 position. Phytase premixes were assayed for phytase activity (U/g) prior to use, based on P-release from Na-phytate. Five pens of four chicks were fed each experimental diet from d 8 to d 22 posthatching. Standard curves were constructed by supplementing graded levels of Pi from KH2PO4 to a P-deficient basal diet containing 0.75% Ca. Assay 1 compared Natuphos r and ECP at a level of 500 U/kg relative to a 3-point standard Pi curve (0, 0.05, 0.10% added Pi). Linear (P<0.05) responses in tibia ash and weight gain resulted from Pi supplementation in all assays. Regression of tibia ash on supplemental Pi intake (r2=0.88) provided a standard curve from which Pi-release values for phytases were calculated. Release of Pi due to Natuphos r and ECP was 0.027% and 0.124%, respectively (P<0.01). Assay 2 compared four graded levels (0, 500, 1,000, and 1,500 U/kg) of ECP and one level of Natuphos r (500 U/kg) relative to a 4-point standard Pi curve (0, 0.05, 0.10, 0.15% added Pi). Based on the regression of tibia ash on supplemental Pi intake (r2=0.97), Pi-release values were 0.125, 0.183, and 0.211% for 500, 1,000, and 1,500 U/kg ECP (quadratic, P<0.05), and 0.037% for Natuphos r at 500 U/kg. Assay 3 consisted of a standard curve (four levels of Pi) and Natuphos r and ECP fed individually at 500 and 1,000 U/kg, or together at 500 U/kg each. Based on the linear regression of tibia ash on supplemental Pi intake (r2=0.97), Pi-release values were 0.041 and 0.153% for 500 U/kg of Natuphos r and ECP, respectively. Supplemented together to achieve 1,000 U/kg, 0.162% Pi was released, while individually, Pi-release values were 0.067 and 0.206% for 1,000 U/kg of Natuphos r and ECP, respectively. Overall, Pi-release values for ECP were approximately four times greater than those for Natuphos r , and no synergism was observed between the two phytases. In a fourth assay, Careleasing efficacy of ECP was evaluated using a 4-point CaCO3 standard curve; 500 U/kg released 0.07% Ca.