The flow of inositol phosphate esters and phytate phosphorus in the proximal and distal parts of the digestive tract of broilers receiving diets adequate in available phosphorus and supplemented with high levels of phytase

Abstract Text: The aim of this study was to characterise the flow of inositol phosphate (iP) esters and disappearance of phytate phosphorus (PP) in the gizzard and ileum of broilers receiving diets adequate in available phosphorus (aP) and supplemented with high levels of phytase. One hundred and sixty-eight Ross 308 broilers at 1 day of age were allocated to 3 treatments (0, 1,500 and 3,000 FTU/kg phytase) in a randomised complete block design, where the pen was the experimental unit (6 birds per pen).  Feed and water were provided ad libitum, and digesta from the gizzard and ileum were collected on day 21 and analysed for iPs and PP relative to TiO₂, the indigestible marker used. In the gizzard, iP6 and iP5 levels were lower (P < 0.01) and inositol higher (P < 0.01) in the diet supplemented with 1,500 or 3,000 FTU/kg phytase compared with the control. In the ileum, supplementation with 1,500 or 3,000 FTU/kg reduced levels of iP6 (3115, 3552, nmol, for 1500, 3000 FTU/kg respectively, P<0.01) and increased that of iP4 and inositol (3115, 3552, nmol for 1500, 3000 FTU/kg, respectively, P < 0.05) compared with broilers fed the control diet (482 iP6, 1650 inositol), except for iP5 which was greater (P < 0.01) in control and with 1,500 FTU/kg phytase compared with 3,000 FTU/kg. There were no phytase effects on IP3 flow. In the gizzard, PP disappearance was greater (P < 0.01) in diets supplemented with 1,500 or 3,000 FTU/kg compared with control diet. No differences were seen in ileal PP disappearance between the control and diet supplemented with 1,500 FTU/kg, or between supplementation of 1,500 and 3,000 FTU/kg; however, PP disappearance was greater in (P < 0.01) diets with 3,000 FTU/kg than control. Total tract PP disappearance was greater (P < 0.05) in diets supplemented with 1,500 or 3,000 FTU/kg (74.5, 85.5,%, respectively) than in the control diet (60.3%). The results show that the phytase rapidly hydrolysed iP6 and iP5 in the gizzard, leading to an accumulation of inositol, and the hydrolysis continued in the distal gut. It is concluded that the phytase was effective in rapidly hydrolysing phytate, releasing free inositol even in the gizzard and that higher phytase doses may lead to further phytate phosphorus hydrolysis in the ileum

Keywords: phytase, inositol phosphate esters, phytate phosphorus