Interactions between supplemented mineral phosphorus and phytase on phytate hydrolysis and inositol phosphates in the small intestine of broilers

Phytate breakdown in the digestive tract of broilers is affected by supplements of mineral phosphorus (P) and phytase with unknown interactions between the 2 factors. It was the objective to study phytate hydrolysis and the presence of inositol phosphate isomers (InsPs) as affected by supplements of mineral P and phytase in the small intestine of broilers. Fifteen-day old broilers were assigned to 48 pens of 20 broilers each (n = 8 pens/treatment). Two low-P corn-soybean meal-based diets without (BD-; 4.4 g P/kg dry matter) or with monocalcium phosphate (MCP; BD+; 5.2 g P/kg dry matter) were supplied without or with added phytase at 500 or 12,500 FTU/kg. On d 24, digesta from the duodenum/jejunum and lower ileum was pooled per segment on a by-pen basis, freeze-dried, and analyzed for P, InsPs, and the marker TiO2. Another 180 broilers (n = 6 pens/treatment, 10 birds each) were fed the 3 BD+ diets from d 1 to 21 to assess the influence of supplemented phytase on tibia mineralization and strength. Significant interactions between MCP and phytase supplements on myo-inositol 1,2,3,4,5,6-hexakis (dihydrogen phosphate) (InsP(6)) hydrolysis (duodenum/jejunum: P <= 0.001; ileum: P = 0.004) and level of specific lower InsPs were detected. Supplementation with 12,500 FTU/kg phytase resulted in 92% InsP(6) hydrolysis and strong degradation of InsP(5). This treatment resulted in higher P net absorption, affirmed by higher BW gain, tibia strength, and mineralization compared to treatments without or with 500 FTU/kg phytase (P <= 0.05). MCP supplementation reduced the degradation of InsP6 and specific lower InsPs in birds fed diets without or with 500 FTU/kg of phytase (P <= 0.05), but did not reduce InsP(6) hydrolysis or degradation of InsP(5) at the high phytase dose. Effects of added MCP on phytase efficacy depend on the dose of supplemented phytase. Differences in the concentrations of lower InsPs indicated that the initial step of InsP(6) hydrolysis is not the only catabolic step that is influenced by MCP or phytase levels.