Phosphorus depletion in sheep and the ratio of calcium to phosphorus in the diet with reference to calcium and phosphorus absorption

Abstract

1. A total of sixty-three wether lambs, 4–6 months old, were fed on diets low in phosphorus and adequate in calcium (0.072–0.073% P, 0.38–0.40% Ca) or adequate in both (0.38–0.40% P, 0.40% Ca) for 134 or 142 days. 2. Concentrations of serum inorganic P and Ca and alkaline phosphatase activity were studied during the depletion period. Bones were taken for histological analysis at the end of the 142 days. 3. After the preliminary depletion period, a metabolism study was conducted in which the effects of previous P depletion and dietary Ca:P ratio upon Ca and P absorption, as measured by isotope techniques, were studied. 4. Histological analysis of bones showed the presence of lesions characteristic of late rickets in some sheep and of severe osteoporosis in others. 5. A wide dietary Ca:P ratio had no apparent effect on P absorption when P intake was adequate. The availability of P was lowered by a diet deficient in P with a wide Ca:P ratio. 6. Previous P depletion resulted in enhanced P absorption during the first 11.5 days after an increased intake of P, but this effect was not shown during days 14–21 after the increase. 7. Ca absorption was reduced by giving a diet low in P and was increased when the intake of P was raised. 8. The response to wide dietary Ca:P ratios by ruminants and non-ruminants is reviewed, and a hypothesis, based upon a knowledge of the intestinal reaction of these species, is offered for the finding that ruminants tolerate wider dietary Ca:P ratios than non-ruminant species.