Effect of Calcium and Phosphorus in Diet of Mothers upon Weight of Young

In spite of an immense amount of work on the retention of calcium and phosphorus under various conditions the amount or ratio of these elements recommended for pregnant or lactating animals is still almost empirical. Before dependable knowledge of the optimal ratio and amounts of these elements during such periods can be obtained numerous animals should be studied through their whole reproductive life. In order to test thoroughly any one calcium and phosphorus mixture it would be desirable (1) to secure as rapid reproduction as possible, and (2) to provide constant quantities of these elements during the animal's entire reproductive history. We have made such a study during the past 2 years, using female rats, and report in this preliminary communication one of our more important findings.

Method. Virgin female rats weighing approximately 200 gm. at 100 days of age, were allowed to raise their first, “qualifying” litter on stock food. The females were remated at the end of 21 days' lactation and placed on the experimental diet.∗ All litters were reduced to 6 pups. When the young were 21 days old they were killed, and the mother immediately remated—thus allowing no rest period between cycles. In this way 10 successive gestations and lactations were studied. Five females were placed on each mineral combination, and the average “success” of the 5 mothers was used as a criterion of the adequacy of the calcium and phosphorus mixture. The “success” of the rats was gauged by averaging, over 10 reproductive cycles, the weight of the young at 21 days of age.