Intestinal and total tract phytate digestibility and phytase activity in the digestive tract of hens fed a wheat-maize-soyabean diet

The intestinal and total tract digestibilities of phosphorus (P) and phytate P were determined in digestibility trials with laying hens and broiler breeders fed a diet containing P, phytate P and Ca at 6.37, 2.00 and 34.1 g·kg^-1, respectively. In both digestibility trials, the total tract digestibility of phytate P was higher than the intestinal digestibility (33 and 35% vs 20 and 18%). In contrast, in both trials the total tract retention of P was lower than the intestinal retention (22 and 19% vs 33 and 35%). Phytate P represented 29.2% of the excreta P of laying hens and 23.6% of the excreta P of broiler breeders. The corresponding proportions of phosphate P were 48.7 and 46.6%, respectively. Samples of digesta and small intestinal mucosa of laying hens were diluted with physiological saline containing sodium phytate and incubated in vitro to determine the phytase activity. The average specific phytase activities in the crop, stomach, small intestinal contents, mucosa and caecal contents were 10.2, 9.2, 14.6, 11.5 and 135 μmol·h^-1·g^-1, respectively. The total phytase activities (per segment) in the small intestine (including the mucosa) and the caeca were 586 and 663 μmol·h^-1, respectively. It can be concluded that phytase activity was present in all sections of the digestive tract. Consequently, in hens fed a wheat-maize-soyabean diet without a phytase supplement, phytate P was partially digestible. A part of the phytate degradation occurred in the hindgut.