Influence of a microbial phytase and zinc oxide on young pig growth performance and serum minerals

Crossbred pigs (n = 288; average age = 21 +/- 3 d and BW = 7.1 +/- 0.2 kg) were used in a 42-d trial to determine the influence of a microbial phytase and various doses of ZnO on growth performance and serum minerals. Pigs (6 castrated males or females/pen) were randomly allotted to treatments in a 2 x 3 factorial arrangement with 2 dietary levels of a microbial phytase (0 or 2,500 phytase units/kg) and 3 dietary levels of supplemental ZnO [0, 1750, or 3,500 mg/kg ZnO (72%Zn)] with 4 pens of castrated males and 4 pens of females per treatment. Diets were formulated to exceed all nutrient requirements, including Ca and P from d 0 to 21 (phase 1) and d 22 to 42 (phase 2). Growth performance, serum Zn, and serum P were not influenced (P > 0.05) by a ZnO x phytase interaction during phase 1, phase 2, or overall (d 0 to 42). Phytase increased (P = 0.01) ADFI and improved (P = 0.02) ADG in phase 1 and improved (P = 0.01) overall ADG, regardless of the level of ZnO supplemented. Zinc oxide supplementation linearly reduced (P = 0.05) ADG, and ZnO at 3,500 mg/kg reduced (quadratic, P = 0.04) G:F in pigs (phase 2). During phase 1, phytase increased serum Ca, but only in the absence of ZnO supplementation, which resulted in a ZnO x phytase interaction (P = 0.02). Serum Zn was increased (linear, P < 0.001) and serum P was decreased (linear, P = 0.05) as ZnO supplementation increased in the diet (phase 1). In phase 2, serum Ca was reduced (linear, P = 0.04) and serum Zn was increased (linear, P = 0.02) as ZnO supplementation increased in the diet. Phytase supplementation increased (P = 0.009) serum Zn and increased (P = 0.003) serum P (phase 1). There was no influence of phytase supplementation on serum minerals in phase 2. In summary, supplemental ZnO reduced growth performance in this experiment. Phytase supplementation improved ADG in Ca- and P-adequate diets regardless of the level of ZnO supplemented, which may be attributed to the reduction of phytate as an antinutrient. In addition, through phytate hydrolysis, phytase reduced phytate-Zn interactions and increased serum Zn, Ca, and P. However, supplementing ZnO increased serum Zn, which reduced serum P and Ca, indicating Ca-Zn-P precipitation. In addition, phytase increased serum Ca, but only in the absence of Zn, further indicating a complex interaction between Zn, Ca, and P in the blood.