Determining the phosphorus release of GraINzyme phytase in diets for nursery pigs

The objective of this study was to determine the available P (aP) release curve for a new phytase source, GraINzyme Phytase (Agrivida Inc., Woburn, MA), which is expressed in corn containing an engineered Escherichia coli phytase called Phy02. Plant-expressed phytases are created by inserting phytase-encoding genes into plants resulting in their ability to produce seeds with increased concentrations of phytase. A total of 360 pigs (Line 200 × 400, DNA, Columbus, NE, initially 9.9 ± 0.19 kg) were used in a 21-d growth study. Pigs were weaned at approximately 21 d of age, randomly allotted to pens based on initial body weight (BW) and fed common starter diets. From days 18 to 21 postweaning, all pigs were fed a diet containing 0.11% aP. On day 21 postweaning, considered day 0 of the study, pens were blocked by BW and randomly allotted to one of eight dietary treatments with five pigs per pen and nine pens per treatment. Dietary treatments were formulated to include increasing aP derived from either an inorganic P source (0.11%, 0.19%, or 0.27% from monocalcium P) or increasing phytase (150, 250, 500, 1,000, or 1,500 FTU/kg). Diets were corn-soybean meal-based and contained 1.24% standardized ileal digestible Lys. On day 21 of the trial, one pig per pen (weighing closest to the mean pen BW) was euthanized and the right fibula was collected to determine bone ash using the nondefatted processing method. Overall (days 0 to 21), pigs fed increasing aP from inorganic P or phytase had increased (linear, P < 0.002) average daily gain (ADG), average daily feed intake (ADFI), and gain-to-feed (G:F; quadratic, P < 0.05). Bone ash weight (g) and percentage bone ash increased (linear, P < 0.001), with increasing inorganic P or added phytase. Based on the composition of the diets used in this study, the release equations developed for GraINzyme for ADG, G:F, bone ash weight, and percentage bone ash are as follows: aP = (0.255 × FTU)/(1299.969 + FTU), aP = (0.233 × FTU)/(1236.428 + FTU), aP = (45999.949 × FTU)/(462529200 + FTU), and aP = (0.272 × FTU)/(2576.581 + FTU), respectively.