Apparently pregnant females were separated from the male and checked daily in the morning for pups in the cage. The first day pups were found was considered the day of birth (day 1). On this day the pups were marked individually by foot pad tattooing and checked for the presence of a milk spot and signs of lack of maternal care. The offspring of 3(wt females were fostered onto 3 (-casein deficient females and vice versa on day 2 (Table 2) , the cross fostered litters being matched for day of birth. The pups were weaned on day 23 by separating them from the nursing female and placing them in cages as described above with same-sex litter mates. From weaning until the age of 6 weeks, water-soaked diet was provided ad libitum in Petri dishes on the cage to weaned pups in all groups to facilitate solid food intake by growth impaired animals.