Abstract
Gnotobiotic broiler chickens were used to study interactive effects of supplemented phosphorus, calcium (PCa), and phytase (Phy) on myo-inositol 1,2,3,4,5,6-hexakis (dihydrogen phosphate) (InsP6) degradation and release of myo-inositol in the digestive tract. In 2 subsequent runs, the chickens were subjected to 1 of 4 dietary treatments with and without PCa and Phy supplementation. Sanitized eggs were hatched in 8 germfree isolators, and a minimum of 9 male Ross 308 chickens were placed in each pen (total 16 pens). Treatments implemented on day 10 included gamma-irradiated diets without (PCa-; 4.1 g P and 6.2 g Ca/kg DM) or with (PCa+; 6.9 g P and 10.4 g Ca/kg DM) monosodium phosphate and limestone supplementation and without (Phy-) or with (Phy+) 1,500 FTU Phy/kg feed in a factorial arrangement. On day 15, digesta was collected from different sections of the intestinal tract and analyzed for InsP isomers and myo-inositol. The isolators did not remain germfree, but analysis of contaminants and results of InsP degradation indicated no or minor effects of the identified contaminants. Prececal InsP6 disappearance was 42% with the PCa-Phy- treatment and 17% with PCa+Phy-. No InsP3-4 isomers were found in the digesta of the terminal ileum in PCa-Phy-. The concentration of myo-inositol in the ileal digesta from PCa-Phy- (6.1 μmol/g DM) was significantly higher than that from PCa+Phy- (1.7 μmol/g DM), suggesting rapid degradation of the lower InsP isomers by mucosal phosphatases and their inhibition by PCa. Phytase supplementation increased InsP6 disappearance and prevented inhibitory effects of PCa supplements (72% in PCa-Phy+ and 67% in PCa+Phy+). However, PCa supplementation reduced the degradation of lower InsP isomers mainly in the posterior intestinal sections in the presence of Phy, resulting in significantly lower myo-inositol concentrations. It is concluded that mucosa-derived phosphatases might significantly contribute to InsP6 degradation in broiler chickens. The potential of mucosa-derived phosphatases to degrade InsP6 and lower InsP is markedly reduced by dietary PCa supplementation.