70 Determination of phosphorus release of Microtech phytase in nursery pig diets

Abstract A total of 320 barrows (DNA 241 × 600; initially 10.7 ± 0.21 kg) were used in a 21-d growth trial to determine the available P (aP) release curve for Microtech phytase (Guangdong VTR Bio-Tech Co, Ltd. Zhuhai, Guangdong, China). At approximately 21 d of age, pigs were weaned and randomly allocated to pens and fed a common diet for 18 d and then fed a P depletion diet (0.11% aP) for 3 d. On d 21 post-weaning, considered d 0 of the study, pigs were blocked by average pen body weight (BW) and randomly allotted to 1 of 8 dietary treatments with 5 pigs per pen and 8 pens per treatment. Dietary treatments were derived from a single basal diet and ingredients including phytase, monocalcium P, limestone, and sand were added to create the treatment diets. Treatments include 3 diets with increasing aP (0.11, 0.19 and 0.27%) using monocalcium phosphate that were used to develop the standard curve and 5 diets with 0.11% aP and increasing phytase (250, 500, 1,000, 1,500 and 2,000 FTU/kg) that were used to develop the aP release curve. Pigs were weighed weekly and feed disappearance was recorded per pen for the calculation of average daily gain (ADG), average daily feed intake (ADFI) and gain to feed ratio (G:F). At the conclusion of the experiment, 1 pig, closest to the mean weight of each pen, was euthanized for bone analysis. The right fibula, rib, and metacarpal were collected for the determination of bone density, bone ash weight, and bone ash percentage. Pigs fed diets with increasing aP from inorganic P had improved (quadratic, P ≤ 0.05) final BW, ADG, and G:F (Table). Pigs fed diets with increasing phytase had linearly increased (P < 0.01) final BW and ADFI and quadratically increased (P ≤ 0.04) ADG and G:F. Bone density, bone ash weight, and bone ash percentage increased linearly (P < 0.01) with increasing aP from inorganic P and increasing phytase. Results were used to determine release values for Microtech phytase for each response criteria as shown in the table. The aP release quadratically increased (P ≤ 0.02) with increasing phytase when growth performance was used as response criteria and linearly increased (P < 0.01) when bone characteristics were used as response criteria. The available P release curve developed for Microtech phytase for percentage bone ash using combined data generated from all three bones is: aP = (0.868 × FTU/kg) ÷ (9,599.511 + FTU/kg).