Determining the phosphorus release of Smizyme TS G5 2,500 phytase in diets for nursery pigs

Two experiments were conducted to determine the available P (aP) release of Smizyme TS G5 2,500 (Origination, LLC., Maplewood, MN) phytase. Pigs were weaned at approximately 21-d of age, randomly allotted to pens based on initial body weight (BW) and fed a common diet. On d 21 post-weaning, pens were blocked by BW and randomly allotted to 1 of 8 (experiment 1) or 7 (experiment 2) dietary treatments with five pigs per pen and eight pens per treatment. Treatments were formulated to include increasing aP from either inorganic P (0.12%, 0.18%, or 0.24% in experiment 1 and 0.11%, 0.19%, or 0.27% in experiment 2 from monocalcium P) or increasing phytase (150, 250, 500, 750, or 1,000 FTU/kg in experiment 1 and 250, 500, 1,000, or 1,500 FTU/kg in experiment 2). Prior to beginning the 21-d studies, all pigs were fed the lowest inorganic P diet for a 3-d period. At the conclusion of each experiment, the pig closest to the pen mean BW was euthanized and fibulas were collected to determine bone ash weight and percentage bone ash. Fibulas were processed using defatted bone mineral procedures. In both experiments, pigs fed increasing aP from inorganic P had increased (linear, P < 0.01) average daily gain (ADG), G:F, and final BW. Additionally, pigs fed diets with increasing phytase had increased (experiment 1 linear, P < 0.01; experiment 2 linear and quadratic, P < 0.05) performance across all growth response criteria. For bone composition, pigs fed increasing aP from inorganic P had increased bone ash weights (linear, P < 0.01) and percentage bone ash (experiment 1 quadratic, P < 0.01; experiment 2 linear, P < 0.01). Similarly, pigs fed increasing phytase had increased bone ash weights (linear, P < 0.01) and percentage bone ash (experiment 1 linear, P < 0.01; experiment 2 linear and quadratic, P < 0.05). The percentage aP released from Smizyme TS G5 2,500 for both experiments varied depending on the response criteria used. As the amount of phytase in the diet increased, the calculated aP release increased when ADG (experiment 1 linear, P < 0.01; experiment 2 linear and quadratic, P < 0.01), G:F (linear, P < 0.01), or percentage bone ash (experiment 1 linear and quadratic, P < 0.05; experiment 2 linear, P < 0.01) were used the predictor variable. When combining the data from experiment 1 and 2, the aP release prediction equations for Smizyme TS G5 2,500 are aP = (0.197 × FTU)/(584.956 + FTU), aP = (0.175 × FTU)/(248.348 + FTU), and aP = (0.165 × FTU)/(178.146 + FTU) when using ADG, G:F, and percentage bone ash, respectively as the predictor variable.