Effect of Phytase Dosage and Source on Growth Performance and Bone Development of Nursery Pigs1

A 28-d growth assay was conducted to determine the effect of phytase dosage and source on growth performance of nursery pigs (initial BW = 10.6 kg). The 9 experimental treatments were control diets (0.13, 0.18, and 0.23% available P) and phytase [100, 225, or 350 phy-tase units (FTU or FYT)/kg] from either Natuphos or Ronozyme P added to the diet containing 0.13% available P. Increasing available P increased (linear, P < 0.01) ADG, ADFI, and G:F. No phytase source × level interactions (P > 0.14) or differences between phytase sources (P > 0.27) were observed. Increasing phytase increased (linear, P < 0.01) ADG and G:F. Increasing available P increased (linear, P < 0.01) bone bending moment. Increasing available P or phytase increased (linear, P < 0.02) percentage bone ash with no difference (P = 0.89) between phytase sources. Regression analysis of the ADG response indicated that when adding 350 phytase units/kg or less, each 100 phytase units/kg will release 0.022 and 0.017% available P for Natuphos and Ronozyme P, respectively Regression analysis of bone bending moment and percentage bone ash indicated that each 100 phytase units/kg will release 0.022 and 0.023% available P for Natuphos and 0.015 and 0.020% available P for Ronozyme P, respectively The results of this experiment indicate that increasing available P or phytase level through 0.23% available P and 350 FTU or FYT/kg, respectively, improves ADG, G:F, and bone criteria.