Sheep nutrition, fetal growth and human health

摘要

It has long been known that impaired size at birth is associated with a high mortality and morbidity, both around the time of birth and subsequently. This is true in domestic animals, wild animals and humans. However recent recognition in human populations that babies bom small are at increased risk of a number of adult diseases, including coronary heart disease and diabetes, has added weight to the importance of research in this field (Barker, 1998). In domestic animals such as sheep it is not hardto demonstrate that limited maternal nutrition results in reduced size at birth. However the dogma has always been that this is not true in humans, and that only exposure to the most severe of famine conditions will result in reduced birth size (Kramer,1987). Furthermore, trials of nutritional supplements in human pregnancy have resulted in minimal effects on size of the offspring (Kramer, 2002). This apparent species difference is more readily understood if it is kept in mind that fetal growth is regulated by fetal nutrition, but thatmaternal nutrition is not the same as fetal nutrition. Nutrition reaches the fetus via a long "supply line" which begins with the maternal diet and metabolism and is affected by the uterine vasculature and placental transport capacity before finally reaching the fetus (Bloomfield & Harding, 1998). Common clinical causes of impaired fetal growth involve interruption of the supply line, resulting in fetal undernutrition even in the presence of normal or indeed excellent maternal nutrition (Harding, 2003).