Calcium and Phosphorus Metabolism in Rats During Pregnancy and Lactation and the Influence of the Reaction of the Diet Thereon

From a quantitative standpoint calcium and phosphorus occupy a foremost place in the list of mineral elements needed by the vertebrate animal organism. The necessity for an adequate supply of these elements is particularly striking during the period of growth and during the lactation period. In pregnancy, the normal adult female, which, prior to the onset of this condition, may be in calcium and phosphorus equilibrium, is required to build new tissue for the fetus and at parturition must secrete milk for the nourishment of the young. Up to the age of weaning, all the food elements obtained by the offspring are derived from the mother’s milk. Experimental work dealing with calcium and phosphorus metabolism during pregnancy and lactation has been carried out chiefly on cows. A few experiments on humans have also been reported. It is well known that heavy producing cows are generally in negative calcium and phosphorus balance. Thus Forbes and his coworkers (1) found that in forty-nine balance trials during liberal milk production without exception all of his animals were in negative calcium balance. Supplementing the diet with additional calcium did not alter the negative balances, indicating that the ability of the animal to absorb calcium is limited. The calcium balances changed from negative to positive during the period of pregnancy when the cows were dry. The phosphorus balances were in most cases negative but not invariably so, indicating that the conditions for the assimilation of this