Effect of dietary phytase level on intestinal phytate degradation and bone mineralization in growing pigs

A pig trial was performed to analyze the effect of different dietary phytase levels on bone mineralization and ileal phytate degradation in 2 different growing stages. Fifty-six postweaned piglets were fed 4 diets differing in P, Ca, Na, and phytase contents. Diets contained either recommended (positive control [PC]) or reduced (negative control [NC]) mineral levels and phytase was added to NC diets at 500 or 2,000 phytase units/kg feed (NC500 and NC2000, respectively). At d 42 and 98, samples (n = 7) were taken for analyses in rib bones (Ca, P, Fe, Mg, Mn, Se, and Zn) and in ileal digesta (myo-inositol phosphates [myo-inositol hexakisphosphate {InsP6}, myo-inositol pentakisphosphate {InsP5}, myo-inositol tetrakisphosphate, and myo-inositol trisphosphate] were analyzed by high-pressure ion chromatography and inositol was analyzed by HPLC). Data were analyzed by ANOVA and means were separated by the Tukey's test with significance set at P < 0.05. Dietary mineral reduction reduced bone mineral content, except in ribs collected at d 42 (P < 0.05). The NC500 diet compared with the NC improved all minerals except Se in ribs (d 98; P < 0.05). The higher phytase dose (NC2000) restored nearly all bone minerals to the level of PC pigs (P > 0.05). Phytate degradation up to the proximal ileum was not influenced by dietary mineral level (PC compared with NC, P > 0.05) whereas phytase reduced InsP6 and InsP5 levels in ileal digesta (P < 0.05 for NC and PC at both phytase application rates) with the lowest levels seen in NC2000 (d 98; P < 0.05). The efficient phytate degradation could explain the improvements in bone mineralization, especially at high phytase application level, probably due to improved mineral availability.