Early weaning does not accelerate the expression of nursing-related taste aversions.

Preweanling rat pups do not display an aversion to a flavor conditioned stimulus (CS) paired with illness if the CS is presented during the act of suckling. In contrast, 20-day-old pups do form such a conditioned taste aversion while suckling (Martin & Alberts, 1979). The dissolution of the nursing-related "blockade" of toxiphobia correlates with the onset of solid food intake. Moreover, prevention of weaning prolongs the blockade; ingestive experience with solid food is necessary for the expression of nursing-related taste aversions in 26-day-old "food naive" pups (Gubernick & Alberts, 1984). The present experiments tested the possibility that premature weaning to solid food might accelerate the onset of nursing-related toxiphobia. Pups were weaned at 13 days of age and ingested only food and water. These prematurely weaned pups received taste aversion conditioning while suckling on Day 16, but showed no aversion to the CS flavor during a later food test. Thus, conditions that lead to early weaning (ingestion of solid food) do not accelerate the onset of taste aversions to mother's milk.