Availability of phytate phosphorus and endogenous phytase activity in the digestive tract of laying hens 20 and 47 weeks old

The availability of phytate phosphorus (P) was determined in 20- and 47-week-old ISA Brown hens fed a maize–soybean meal diet. Phytate P determined by a capillary isotachophoretic method represented 0.358 of the total P of the feed. The availability of phytate P was higher (P<0.001) in 47-week-old (0.53) than in 20-week-old (0.24) hens. The excreta of the older hens contained significantly less phytate P (3.1 mg g DM−1) than that of the younger hens (4.5 mg g DM−1), with the proportion of phytate P in the total faecal P 0.15 and 0.24, respectively. Samples of digesta and intestinal mucosa were diluted with physiological saline containing sodium phytate and incubated anaerobically to determine in vitro phytase activity. Specific activity (per g) in the stomach, intestinal mucosa and caeca was higher (P<0.05) in 47-week-old hens (6.7, 12.1, 143.2 μmol h−1, respectively) than in 20-week-old hens (3.3, 7.0, 103.2 μmol h−1, respectively). A relatively high total phytase activity was found in the caeca of both young (347 μmol h−1) and old (632 μmol h−1) hens compared to that in other digestive segments, with little activity in the stomach (47 and 102 μmol h−1, respectively) and intermediate in the small intestine (226 and 264 μmol h−1, respectively).