Voluntary exercise during pregnancy and lactation and its effect on lactational performance in mice.

The amount of voluntary exercise during pregnancy and lactation and its effect on the lactational performance in mice were investigated. Female mice were housed in exercise cages with treadwheels during periods of growth, pregnancy and lactation and the amounts of exercise were measured. It was observed that growing female mice exercised voluntarily at a level of approximately 5,000 rotations (diameter of treadwheel; 13.5 cm) per day during the 4-week growth period. After conception, the amount of exercise gradually decreased and in late pregnancy running activity decreased markedly. Throughout the lactational period dams exercised lightly. As indices of lactational performance, the body weights of pups nursed in litters of 8, milk yield and cellular development of abdominal-inguinal mammary glands were examined. There were no significant differences in the final body weights of pups, milk yield per day or development of mammary glands between exercise and non-exercise groups.