Hydrolysis of phytate and formation of inositol phosphate isomers without or with supplemented phytases in different segments of the digestive tract of broilers

The objective was to characterise degradation of myo-inositol 1,2,3,4,5,6-hexakis (dihydrogen phosphate) (InsP6) and formation of inositol phosphate (InsP) isomers in different segments of the broiler digestive tract. Influence of an Aspergillus niger (PhyA) and two Escherichia coli-derived (PhyE1 and PhyE2) phytases was also investigated. A total of 600 16-d-old broilers were allocated to forty floor pens (ten pens per treatment). Low-P (5·2 g/kg DM) maize-soyabean meal-based diets were fed without (basal diet; BD) or with a phytase added. On day 25, digesta from different digestive tract segments were pooled per segment on a pen-basis, freeze-dried and analysed for P, InsP isomers and the marker TiO2. InsP6 degradation until the lower ileum (74 %) in BD-fed birds showed a high potential of broilers and their gut microbiota to hydrolyse InsP6 in low-P diets. Different InsP patterns in different gut segments suggested the involvement of phosphatases of different origin. Supplemented phytases increased InsP6 hydrolysis in the crop (P < 0·01) but not in the lower ileum. Measurements in the crop and proventriculus/gizzard confirmed published in vitro degradation pathways of 3- and 6-phytases for the first time. In the intestinal segments, specifically formed InsP4-5 isomers of supplemented phytases were still present, indicating further activity of these enzymes. Myo-inositol tetrakisphosphate (InsP4) accumulation differed between PhyE1 and PhyE2 compared with PhyA in the anterior segments of the gut (P < 0·01). Thus, the hydrolytic cleavage of the first phosphate group is not the only limiting step in phytate degradation in broilers.