Phytase inclusion in pig diets improves zinc status but its effect on copper availability is inconsistent

Complexation of dietary phytate with cations is a major cause of reduced bioavailability of Zn and possibly Cu in pig diets. We conducted 2 studies with 2 treatments in young growing pigs (8 to 40 kg) to estimate potential contributions of phytase to availability and supply of Zn and Cu, respectively. Each treatment comprised 10 pens with 8 pigs each as experimental units. In Exp. 1, 500 phytase units (FTU)/kg of microbial phytase (Natuphos 5000G; BASF) was added to a diet containing 15 mg Zn from ZnSO4 and 160 mg/kg Cu from CuSO4 in addition to Cu and Zn from feed ingredients. In Exp. 2, 500 FTU/ kg was added to a diet containing 45 mg Zn from ZnSO4 without added CuSO4. Feces were collected to determine nutrient digestibility, blood was collected, and pigs were killed to determine Cu and Zn in the liver. In both experiments, phytase inclusion increased (P < 0.001) Zn digestibility by on average 10% units, serum Zn level (P < 0.001) by 0.4 mg/L, and liver Zn content (P < 0.001) by 129 mg/kg DM. In Exp. 1 phytase increased (P = 0.03) Cu digestibility by 6% units but reduced (P = 0.04) liver Cu content by 35 mg/kg DM. In Exp. 2 phytase reduced (P < 0.001) Cu digestibility by 16% units without affecting liver Cu content. Results indicate that the effect of phytase on Cu availability depends on dietary Cu and Zn content and the response variable studied. In conclusion, the consistent effects of phytase on indices of Zn status allow a reduction of Zn inclusion in phytase-supplemented diets.