Comparative aspects of prepartum maturation: Provision of nutrients

Abstract

SummaryAt birth, the pattern of nutrition changes from a continuous but limited supply of nutrients from the placenta to an intermittent yet more plentiful provision of metabolic substrates via the gut. The success of this transition from parenteral to enteral nutrition depends on adequate fuel reserves, functional mechanisms for regulating nutrient utilization and production, a gastrointestinal tract competent at digestion and sufficient motor development to allow suckling. Maturational changes in key tissues (eg liver, gut) and endocrine systems (eg pancreas, adrenal) therefore occur during late gestation in preparation for the nutritional transition at birth. In many species, these maturational changes are dependent on the prepartum increase in cortisol secretion by the fetal adrenal. In fetal sheep, cortisol has been shown to stimulate hepatic glycogen deposition, induce hepatic gluconeogenic enzymes and adrenoreceptors and accelerate the structural and functional development of the gut. In fetal horses, prepartum maturation of the glucogenic and glucoregulatory capacities occurs comparatively late in gestation coincidentally with the natural rise in fetal plasma cortisol which occurs much closer to term in this than other domestic species. The relatively narrow window for glucocorticoid dependent maturation in the foal has consequences for survival both in utero in response to adverse conditions and at birth. Fetal foals are unable to produce glucose endogenously during late gestation and develop severe hypoglycaemia if delivered prematurely. Foals born with low cortisol levels therefore adapt poorly to extrauterine life while, conversely, increasing fetal glucocorticoid levels by betamethasone administration or by stress induced fetal cortisol secretion can lead to early delivery of viable foals which are normoglycaemic and able to digest enteral feeds. Increase prenatal exposure to glucocorticoid therefore appears to be as much a prerequisite for the neonatal transition from parenteral to enteral nutrition in the horse as it is in other species. Keywords

The effects of maternal health and body condition on the endocrine responses of neonatal foals

“…In the current study, there was a fall in maternal glucose concentrations during the period of inappetence and weight loss caused by Streptococcus equi infection and glucose concentrations tended to be lower in the moderate nutrition group. Since the fetal glucose supply depends on maternal glucose levels and has a more important role in fetal oxidative metabolism in the horse than other species (Fowden et al 2001), the fetuses of the moderately nourished group were probably glucose deprived and metabolically compromised during the period of maternal inappetence. Changes in glucose availability may, therefore, have an important role in programming the number or sensitivity of the β cells in the equine pancreas during intrauterine development.…”

Programming placental nutrient transport capacity

“…They also produce lactate for fetal use and metabolize amino acids by deamination and transamination as part of a multiorgan system supplying essential and gluconeogenic amino acids to the fetus (Hay, 1995; Regnault et al 2005). The fluxes of carbohydrates and amino acids into and across the ovine placenta are responsive to a range of environmental factors including nutritional state, placental size, temperature and hormone concentrations (Owens et al 1989; Liu et al 1994; Harding et al 1997; Ross et al 1996; Timmerman et al 2000; Fowden et al 2001). Early glucocorticoid exposure in sheep increases uteroplacental glucose consumption and reduces the absolute amount and proportion of glucose taken up by the uterus that is delivered to the fetus (Barbera et al 1997; Ward et al 2004).…”

Glucagon, insulin, adrenocorticotropic hormone, and cortisol in response to carbohydrates and fasting in healthy neonatal foals

“…These adaptations are accompanied by changes in the hypothalamus‐pituitary‐adrenal axis (HPAA), energy metabolism, and cardiovascular system 3‐6 . The endocrine pancreas must assume its glucoregulatory role after birth to maintain euglycemia, 7 as neonatal foals transition from intrauterine parenteral to extrauterine enteral nutrition 8 . The endocrine pancreas of the equine fetus is functionally mature before birth 9,10 .…”

“…[3][4][5][6] The endocrine pancreas must assume its glucoregulatory role after birth to maintain euglycemia, 7 as neonatal foals transition from intrauterine parenteral to extrauterine enteral nutrition. 8 The endocrine pancreas of the equine fetus is functionally mature before birth. 9,10 It can secrete insulin in response to glucose and amino acids, and is believed to be important in regulating fetal nutrient utilization and growth.…”