Changes in body weight and food intake were studied for 14 days post partum in primiparous rats.
The growth increments in suckled rats with galactophores cut to prevent milk withdrawal and in normally lactating rats were greater than in unsuckled controls. The growth increments in rats with galactophores cut were accompanied by parallel increases in food intake.
Injection of 3 i.u. prolactin daily did not reproduce these changes in body weight and food intake in non-suckled rats.
The results suggest that the main factor in the extra growth of lactating rats is an increased food intake in excess of the metabolic needs for milk secretion induced by the stimulus of suckling.