Calcium metabolism in pregnant ewes.

I . A combination of balance and isotope techniques has been used to study calcium metabolism in ten sheep at different stages of pregnancy, and the results have been combined with earlier results obtained during lactation to show the variations in Ca metabolism which occur during the whole reproductive cycle. 2. Transfer of Ca to the foetuses during pregnancy and to the milk after parturition rose rapidly from the 65th day of gestation and reached a maximum at parturition or shortly afterwards. 3. Although the rate of absorption of Ca from the intestine increased steadily throughout pregnancy it was insufficient to meet the full requirements of late pregnancy and early lactation. During this period, the extra Ca was supplied by increased bone resorption. 4. The maternal Ca balance became negative duringpregnancy, the net dailyloss of Careaching a maximum in early lactation. 5 . In late lactation the maternal Ca balance became positive enabling the animals to replenish their skeletal stores. 6. There was no marked change in the demands for Ca at parturition and the connexion between this observation and the pathogenesis of milk fever is discussed. 7. Rates of transfer of Ca to the foetus during pregnancy are compared with estimated values of other workers.