The Role of Calcium and Phosphorus in Determining Reproductive Success

Abstract

One hundred and forty-five female rats (who gave birth to 8431 pups, and raised 4391 to 21 days of age) have been studied for ten consecutive reproductive cycles while receiving a diet of purified foodstuffs containing a constant quantity, but varying levels and ratios, of calcium and phosphorus. Both level and ratio of mineral elements exerted an effect on the success of the mothers in producing and rearing young. A Ca/P ratio of 1.0, at a calcium level of 0.490 per cent, was adjudged (on the basis of weight of young at 21 days, ash content of the young, and change in weight of the mothers) the ideal mineral level and ratio for successful gestation and lactation in rats. By employing the average weights of 21-day-old young it was shown that the optimal ratio depends upon, and is proportional to, the calcium level. If the calcium intake is not known exactly, a Ca/P ratio of 1.0 will approximate the optimal. At excessive mineral levels (2.45 per cent) poor performance was obtained, irrespective of ratio. The largest ash contents of the 21-day-old young were uniformly obtained when the mother rat received a diet with Ca/P ratio of 1.0. At constant phosphorus intake (0.245 per cent), increasing the calcium content of the mothers' diet from 0.017 to 0.490 per cent gave better reproductive success; further calcium increases made for rachitic diets and failure. Phosphorus (PO₄) in excess was better tolerated than calcium in excess. The relationship of these findings to human nutrition has been discussed.