PSI-16 Effect of HiPhorius phytase on finishing pig growth performance and bone mineralization with the use of two diet formulation strategies

Two experiments were conducted to determine the effect of HiPhorius (dsm-firmenich, Parsippany, NJ) phytase on finishing pig growth performance, serum chemistry, bone mineralization, and carcass characteristics. In Exp. 1, 1,161 pigs (PIC 337 × 1050, initially 36.7 ± 0.48 kg) were used in a 105-d trial. There were 27 pigs per pen and 10 or 11 replications per treatment. Treatments consisted of: 1) Control diet with no added phytase and formulated to NRC (2012) requirement estimates for standardized total tract digestible (STTD) P; 2) 600 FYT/kg added phytase formulated to the same STTD P as the control diet considering a release of 0.13% STTD P and 0.095% STTD Ca; 3) 1,000 FYT/kg added phytase formulated to the same STTD P as the control diet considering release of 0.16% STTD P and 0.107% STTD Ca, and 4) high STTD P (no phytase; approximately 22% above NRC requirement estimates). All diets were formulated to a 1.30:1 STTD Ca:STTD P ratio, but analysis suggested all phases were greater than the formulated target. Overall, pigs fed NRC (2012) or increased STTD P had increased average daily gain (ADG) and hot carcass weight (HCW; P < 0.05) compared with pigs fed the treatments with added phytase. Pigs fed NRC (2012) STTD P had greater (P < 0.05) gain to feed ratio (G:F) compared with those with 1,000 FYT/kg with other treatments intermediate. In Exp. 2, 1,160 pigs (PIC 337 × 1050, initially 75.9 ± 1.32 kg) were used in a 58-d trial. There were 27 pigs per pen and 11 replications per treatment. Treatments were the same as in Exp.1 except diets were formulated to the same total Ca:P ratio [1.15:1 from 75 to 100 kg and 1.12:1 from 100 to 136 kg body weight (BW)] without a STTD Ca release consideration from phytase; however, diets analyzed with a wider Ca:P compared with the expected value (Table 1). Overall, there were no differences in ADG, average daily feed intake (ADFI) or G:F among treatments (P > 0.10). For pigs fed NRC or increased STTD P, there was an increase (P < 0.05) in metacarpal bone density, and a tendency for increased (P < 0.10) bone ash weight and percentage bone ash compared with pigs fed treatments containing phytase. In conclusion, regardless of diet formulation strategy, pigs fed diets with phytase had decreased growth performance (Exp.1) and bone mineralization (Exp.2), which was unexpected and could be a result of the nutrient release values attributed to the phytase being overestimated, not enough phytate-bound P that is phytase-sensitiv