THE EFFECT OF DIETARY CALCIUM ON THE EXCRETION OF CALCIUM, MAGNESIUM AND PHOSPHORUS IN RATS FED ON PURIFIED FELINE DIETS

In this study, the previously reported effects of dietary calcium leve l on mineral excretion in ovariectomized cats were compared with those in rats. Rats of a physiological age similar to that of the cats were used and they were fed similar feline diets according to the same fee ding schedule. The female rats, which were ovariectomized at the onset of sexual maturity, were fed purified diets containing either 3.2, 4. 8, 9.5 or 19.3 mmol calcium/MJ in a a-week parallel study. To evaluate any effect of ovariectomy, sham-operated rats were also used. In the rats, in contrast with the cats used earlier, urinary calcium concentr ation rose with increasing calcium intake, but urinary magnesium conce ntration was not systematically affected. Urinary concentrations of ph osphorus dropped when the rats were fed diets with increasing calcium levels. The percentages of apparent absorption of phosphorus and magne sium fell when calcium intake was raised; the percentage of calcium ab sorption was also slightly lowered. Apparent absorption percentages fo r calcium, phosphorus and magnesium were higher in the rats, when comp ared with the cars used earlier. Ovariectomy in the rats had no signif icant effect on calcium-induced mineral excretion.