Site of Phosphorus Absorption from the Intestine of the Horse

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Abstract
The site of phosphorus absorption was studied by comparing the absorption of 32P placed directly into the cecum of fistulated ponies, with that absorbed from an intragastric dose and by estimating apparent absorption in different areas of the intestinal tract of ponies using Cr2O3 as an unabsorbable marker. There was no difference in the absorption of 32P following gastric or cecal administration indicating that phosphorus may be absorbed from the large intestine. The Cr2O3/nutrient ratio technique indicated that phosphorus was secreted into the upper half of the small bowel and that a nearly equal amount was absorbed from the lower half of the small intestine. There was a large flux of phosphorus into the cecum and net absorption from the dorsal colon and from the small colon. The major sites of net phosphorus absorption from all feed sources were the dorsal large colon and the small colon. The calcium content or the type of feedstuff did not affect the site of absorption.