Role of dietary preferences in the weaning pattern of the rat

Weaning in the rat begins on postnatal day 17 and is completed by day 26. To evaluate the contribution of dietary preferences and/or aversions to weaning progression, choice experiments utilizing isocaloric liquid diets were conducted. In experiment 1, both consumption records and behavioral studies showed that pups choosing between two diets differing only in the nature of the carbohydrate (CHO) (glucose vs. lactose) had a strong preference for the glucose diet. In experiment 2, pups chose between diets differing in the relative proportions of CHO and fat. When the CHO was glucose, the preference was for the high-CHO diet, whereas when the CHO was lactose, the preference was for the low-CHO diet. The sweetness preference and/or lactose aversion of these experiments was present from day 17 onward and therefore cannot explain the gradual transition seen in normal weaning. In experiment 3, behavioral testing showed that pups choosing between suckling from their anesthetized dam or drinking a liquid diet strongly preferred to suckle at day 17 but to drink by day 24. The gradual transition displayed in this experiment suggests that the decline of interest in suckling plays an important role in the process of weaning.