Forage availability should cover most needs for mares bred during spring and summer. Out-of-season breeding, lack of access to pasture, or good quality forage calls for nutritional supplementation. Current evaluations of broodmare needs are based on fetoplacental tissue requirements, but do not consider endocrine changes or that the maternal diet quality affects long-term foal health. This article reviews pregnant mares' current nutritional recommendations. Secondly, fetoplacental developmental stages during gestation are outlined, defining critical periods in the context of the developmental origins of health and disease. Last, examples of how maternal nutrition affects long-term foal health are presented.