EFFECTS OF A CHANGE IN PHOSPHORUS REQUIREMENT ON PHOSPHORUS KINETICS IN THE SHEEP

An experiment was carried out to examine the effects of a change in P requirement, achieved by intravenous calcium loading, on intestinal ph osphorus absorption, salivary phosphorus secretion and faecal endogeno us phosphorus loss in adult sheep fitted with a rumen and duodenal can nula. Isotope dilution was used to measure faecal endogenous phosphoru s loss while (103)ruthenium phenanthroline and (51)chromium ethylenedi amine tetra-acetic acid were used to measure duodenal phosphorus flow. The infusion of calcium chloride led to an increase in calcium and ph osphorus retention, the increase in phosphorus retention being due to a reduction in faecal phosphorus excretion as a result of enhanced int estinal phosphorus absorption and reduced faecal endogenous phosphorus excretion. There was, however, no change in duodenal phosphorus flow or in the amount of phosphorus estimated to have been added to the dig esta via the saliva. These results suggest that the increase in phosph orus retention seen in response to an increase in phosphorus requireme nt is largely achieved through an increase in intestinal absorptive ef ficiency and not through any reduction in endogenous phosphorus secret ion into the gut.