Phytase calcium digestibility

Traylor, S.L. G.L. Cromwell M.D. Lindemann D.AKnabe. Effects of level of supplemental phytase on ileal digestibility of AAs, calcium, and phosphorus in dehulled soybean meal for grow-... 

Mellanby (1950), who also saw differences in phytic acid digestion in his puppies, discusses various possible explanations of the observed effect. One is that vitamin D should increase phytase secretion into the intestines. Another is that vitamin D acts on the phytic acid via calcium. 

To the authors of this review the second h3rpothesis offers a reasonable explanation of the effect observed. It is well known that, other conditions being equal, extra calcium in the diet depresses phytic acid digestion in man (Cruickshank et al., 1945), in rats (Lowe and Steenbock, 1936), and in puppies (Mellanby, 1949, 1950). In vitamin D deficiency the absorption of calcium is decreased. More calcium will be present in the intestinal content and will counteract the phytic acid digestion, partly by an inhibitory action on the phytase and partly by precipitating more phytic acid. 

A method of study suggests itself. Animals should be fed a diet free of calcium in the periods of exploration of phytic acid digestion. The rat, which has measurable quantities of phytase in the mucous membrane of the small intestine but in which the phytic acid digestion is still incomplete, is clearly the animal to be used. 

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