The effects of phosphorus depletion, and of calcium and phosphorus intake, on the endogenous excretion of these elements by sheep

Abstract

1. Injections of 32P and 45Ca were used to study the influence of phosphorus depletion and repletion on the rates of endogenous calcium and P excretion in fifteen P-depleted and eighteen control sheep. 2. When given adequate P, there was a marked increase in the rate of excretion of metabolic faecal P in sheep which previously had been depleted. In control sheep a decrease was found in metabolic faecal P excretion with a diet deficient in P. 3. From the values for metabolic faecal P an indirect estimate of total intestinal secretion was made. The estimate was found to be in approximate agreement with values derived from published values for total daily digestive secretions in sheep. 4. The estimated rates of secretion of intestinal P suggest that after the addition of P to the diet the changes in the rate of excretion of metabolic faecal P in P-depleted sheep were the result of a decreased reabsorption of intestinally secreted P rather than of a change in the rate of secretion into the intestine. After a diet low in this element the decrease in metabolic faecal P excretion by control sheep appeared to be the result of a decreased rate of intestinal P secretion. 5. The possible significance of changes in metabolic faecal P excretion in relation to body P homoeostasis in the ruminant animal is discussed.