Impact of super-dosing phytase on growth performance, energy and nutrient utilization, and phytate breakdown

The objectives of these experiments was to evaluate super-dosing phytase as a way to enhance growth performance of growing pigs and to understand the mechanism behind the performance improvement. One experiment used 440 pigs (6.27 ± 0.01 kg) in a 2 × 2 factorial treatment design comparing the main effects of diet (NRC derived positive control [PC] versus a negative control: 10% lower SID lysine and 1% reduced fat [NC]) and phytase levels (0 vs 2,500 FTU phytase). Phytase improved ADG and G:F (P \u3c 0.05). Experiment 2 was conducted on 2,200 growing pigs (36.6 ± 0.3) allotted to 5 treatments: a balanced PC (250 FTU phytase/kg), a NC (15% less SID lysine and 1.5% lower NE), and 3 SD treatments applied to the NC for a total of 1,000, 1,750, and 2,500 FTU phytase/kg. Phytase improved carcass feed and energy efficiency (P \u3c 0.05). The 3 remaining experiments used 32 gilts fitted with t-cannulae at the terminal ileum (39.7 ± 0.3 kg, 60.5 ± 0.5 kg, and 82.5 ± 0.7 kg, for Exp. 3, 4 and 5, respectively) allotted to 4 treatments: a corn-soy control diet containing 250 FTU phytase/kg, and 3 SD treatments with phytase added to 1,000, 1,750, and 2,500 FTU phytase/kg, respectively. Chromic oxide was added at 0.4% as a marker. In Exp. 3, SD increased the apparent ileal digestibility (AID) of ether extract and dry matter (DM), decreased the apparent total tract digestibility (ATTD) of phosphorus and decreased calcium excretion (P \u3c 0.05). In Exp. 4, SD increased the ATTD of nitrogen and DM, and decreased calcium excretion (P \u3c 0.05). In Exp. 5, SD increased the AID of DM, GE, and starch, and decreased the ATTD of phosphorus and calcium, and decreased calcium excretion (P \u3c 0.05). Super-dosing phytase decreased the concentration of phytate and inositol-5-phosphate, and increased the concentration of lower inositol derivatives and myo-inositol in Exp. 3, 4, and 5 (P \u3c 0.05). Therefore, the growth improvements observed with SD are unlikely a result of improved nutrient or energy digestibility, but may be related to phytate degradation and increased myo-inositol availability