Abstract
This study aimed to investigate the effect of phytase and a combination of phytase and xylanase on the prececal phosphorus digestibility (pcdP) of wheat-based diets in turkeys. A low-P basal diet (BD) based on cornstarch and soybean meal, and 2 diets containing 43% of different wheat genotypes (genotype diets GD6 or GD7) were fed to turkeys from 20 to 27 d of age. Diets were fed either without enzyme supplementation or supplemented with phytase (500 FTU/kg) or a combination of phytase and xylanase (16,000 BXU/kg). At 27 d of age, digesta were sampled from the lower ileum of animals to determine pcdP and pc myo-inositol 1,2,3,4,5,6-hexakis (dihydrogen phosphate) (InsP6) disappearance, and to analyze the concentrations of lower inositol phosphate isomers. Similar pcdP was observed in non-supplemented BD and GD (∼36%). Phytase alone increased the pcdP in all diets by 8 to 12%, but a beneficial effect of xylanase was found only for BD. Similar results were found for pc InsP6 disappearance, although xylanase addition compared to phytase alone decreased pc InsP6 disappearance in GD7 compared to phytase alone. Animals fed GD7 performed better than those fed GD6; however, these differences could not be linked to the pcdP. The pattern of lower inositol phosphates in digesta also changed with enzyme supplementation, resulting in lower proportions of InsP5 and higher proportions of InsP4. Phytase alone decreased Ins(1,2,3,4,6)P5 but increased D-Ins(1,2,3,4,5)P5 and D-Ins(1,2,5,6)P4 concentrations. An additional increase in D-Ins(1,2,3,4,5)P5 and D-Ins(1,2,5,6)P4 concentrations was achieved with xylanase, although for the former isomer, this was observed only with GD. These results indicate that enzyme supplementation alters the pc degradation of InsP6, and that combining both enzymes had a minor additional effect on the pcdP from wheat-based diets when compared to phytase alone.