Effect of short-term removal of infant rats from the female on lactation.

Removal of the young for a single period of at least 12 hours at the age of 15 days led to a marked increase in 85Sr retention in the maternal organisms and to a decrease in its transfer to the young in the milk. Study of 85Sr transfer in the milk showed that, if the litter was completely changed on the 16th day after birth, the female immediately accepted foster young. Repeated removal of the young on the 14th day and 15th day of life for a length of time which had no effect in a single removal likewise led to a decrease in 85Sr transfer in the milk and to raise 85Sr retention in the female. The gradual decrease which occurs in lactation during the weaning period is probably caused by diminution of the suckling stimulus on the part of the young, as they lose their physical dependence on the female.