Abstract
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
Highlights
The most striking observation shown is the fact that in seventeen lactation periods on the various diets all show that the animals were in negative calcium balance
In sixteen periods the phosphorus balances were negative and in only one period was the animal in phosphorus equilibrium
Our experiments have indicated a storage of calcium and phosphorus during pregnancy
Summary
The period of pregnancy is comparatively short, the onset of pregnancy can be definitely ascertained, the lactation period is likewise of short duration, the calcium and phosphorus content of the young at the time of weaning can be determined, the experimental animals can be kept for long periods of time on a constant diet, and the excreta can be collected. Since the experiments yielded the information that during the lactation period the dietary requirements of the rat for calcium and phosphorus are increased, we have used the opportunity to study the effect of varying the reaction of the diet upon the absorption of these elements by both mother and offspring. Calcium was determined by McCrudden’s method and phosphorus by the method of Pemberton-Kilgore
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