Behavioral and physiologic effects of early nutrition and social factors in the rat

Two experimental methods to provoke caloric restriction during suckling were used. Each of the methods utilized two different rat groups: Low Growth (LG) and High Growth (HG). In one method, the groups also differed in a social factor, litter size: crowded (Cr) and control (Co). Growth differences and high levels of social competition were found among pups of the crowded group with Low Growth (CrLG) compared to the group with High Growth and small litters (CoHG). Both methods resulted in growth differences between respective groups from the first week of suckling. Differences in animal groups persisted forty days after weaning. LG animals had higher defecation scores with lower activity in the open-field test, higher susceptibility to restraint ulcers and adrenal hypertrophy than HG rats, in litters of equal size. However, early stimulation from social competition among pups in larger different litters in CrLG group counteracted nutritional factor effects. Elevated open-field defecation and ulceration scores with adrenal hypertrophy were found in CoHG rats.