RESUMEN
1. In order to study the effects of protein quantity and quality on development, Wistar rats were submitted to four different diets during lactation and post-lactation periods. Three isocaloric diets were utilized with 6 per cent (M), 16 per cent (W16) and 20 per cent (W20) of protein (casein), and the fourth diet (C) consisted of a commercial lab chow containing 22 per cent protein. 2. During the lactation and post-lactation periods the body weights of dams and pups were recorded weekly. On the 49th day of age (21 days of suckling and 28 days of ad libitum chow), all animals were sacrificed and the brains removed and weighed. 3. Dams from all groups increased food intake during the lactation period, but dams of the M group consumed a lower amount of diet as compared with other groups. Only the body weight of M dams was affected by diet during the lactation period, but the body weight of pups from the M and C groups was lower than in the other two groups. At 49 days of age C and M pups showed a significantly lower brain weight compared with W16 and W20 pups. 4. Thus, a commercial lab chow diet does not promote normal body and brain development as compared with balanced diets containing 16 or 20 per cent protein. These results emphasize the need for further studies in order to evaluate other biological and behavioral parameters that might be altered by a lab chow diet