The role of dietary phytate (inositol hexaphosphate) in the regulation of intestinal mucosa phytase was investigated in chicks. Seven-day-old chicks were grouped by weight into six blocks of three cages with six birds per cage. Three purified diets [a chemically defined casein diet, a chemically defined casein diet plus sodium phytate (20 g/kg diet) and a chemically defined casein diet plus sodium phytate (20 g/kg diet) and microbial phytase (1000 units/kg diet)] were randomly assigned to cages within each block. Chicks were fed experimental diets from 8 to 22 days of age then killed, and duodenal mucosa and left tibia removed. Phytase activity in duodenal mucosa, growth performance and bone ash content were determined. Addition of phytate to the chemically defined casein diet reduced (p < 0.05) the Vmax of the duodenal brush border phytase, but the Km of the enzyme was not affected. Addition of phytate also reduced (p < 0.05) weight gain, feed intake, feed efficiency and percentage ash. Addition of microbial phytase fully restored the feed efficiency (p < 0.05), but Vmax and body weight gain were only partially restored (p < 0.05). In conclusion, it would seem that dietary phytates non-competitively inhibit intestinal mucosa phytase.

An investigation into the influence of phytates on the in situ absorption of amino acids (lysine, glutamate and leucine) and glucose from the intestinal lumen of 3-week-old chickens was carried out. Birds were anaesthetised and the intestines exteriorised. Uptake of 5 mM of each nutrient over a 4-min period was measured in the presence of four phytate concentrations (0, 50, 250 and 500 mM). Five birds were used for each nutrient at each concentration of phytate tested. Leucine uptake decreased linearly (P < 0.001) and that of glutamate showed a tendency to decrease (P = 0.055) as the phytate concentration increased. Absorption of lysine and glucose were unaffected by the presence of phytate. In conclusion, phytate in the small intestinal lumen exerted a depressive effect on the absorption of specific free amino acids from the lumen. Its depressive effect was greatest for leucine followed by glutamate, and phytate had little effect on the absorption of lysine.