LASTING BIOLOGICAL EFFECTS OF EARLY ENVIRONMENTAL INFLUENCES

Newborn specific-pathogen-free mice (SPF) were separated from their mothers shortly after birth and immediately reallocated at random to foster mothers, each of which received eight young. Under these conditions, the growth rate and adult size of the young were profoundly and lastingly conditioned by some unidentified influence exerted by the foster mother. In SPF mice nursed by their own mothers, the diet of the latter during gestation and lactation, or during lactation alone, conditioned the weight of the young at weaning time, and throughout their whole life span. Lasting depression of growth has been achieved by minor alterations of the dam's diet, for example by lowering its content in magnesium, or in lysine and threonine. The growth-depressing effect so achieved persisted throughout the whole life-span of the young, even though they were given at weaning time and constantly thereafter unlimited amounts of an optimum diet. In contrast, the weight-depressing effect of a diet deficient in lysine and threonine administered to adult animals was completely and rapidly reversible when a complete diet was later substituted for the deficient one. Depression of growth resulting from nutritional experiences during gestation or lactation did not seem to affect adversely the health of the young, or to decrease their longevity. In fact, the results of two experiments in which the animals nursed by mothers on different diets, were kept undisturbed and on optimum diets throughout their whole life span, suggest that the smaller animals had a greater average life expectancy than the larger ones.