ABSTRACTFetal programming by undernourishment refers to the effects of early life subnutrition on organ development later in life. Sheep breeding in Uruguay occurs normally in autumn, with parturitions in late winter or early spring. Since pasture production and quality is lowest in winter, most pregnant sheep are subject to nutrient restriction. We hereby present four experiments which describe deleterious effects of undernourishment during gestation on reproductive organs development of the lambs. We hypothesized that intrauterine subnutrition affects reproductive organs development in male lambs. Three experiments were carried out on natural pasture in Uruguay, and one of them was carried out under indoors, controlled conditions. Our results on 70 day fetuses, newborn lambs, as well as 100 and 200 days old lambs indicatethat subnutrition during early life determines smaller testes and external genitalia, lower scrotal circumference, and lower numbers of Sertoli cells which may limit the reproductive potential of rams in adulthood.