Prenatal gastrointestinal development in the pig and responses after preterm birth

Despite clinical research and medical advances, care of the preterm infant remains a clinical challenge, with the immature gastrointestinal (GI) system limiting the types and amounts of nutrients that can be provided enterally to meet energy and nutrient requirements. Progress in understanding the relationship between dietary inputs and the developing GI system after preterm birth has been limited by ethical constraints of using preterm infants as experimental subjects and a lack of relevant animal models. We review development of the GI system of the pig during gestation, the similarities shared with human fetuses, and the responses to dietary stimuli. The GI systems of pigs and humans develop early in gestation, with growth and maturation accelerating during the final weeks prior to birth. As a consequence, deficits in GI digestive capacities are directly related to how early in gestation an infant or pig is delivered, thereby complicating attempts to provide adequate enteral nutrients for growth and development. Pigs differ from humans by being born with low activities of the brush border membrane carbohydrases necessary for hydrolysis of nonlactose carbohydrates. Fetuses of both species have impaired lipid digestion coinciding with lipid malabsorption after preterm birth. Protease activity, although present, may not be adequate and may limit growth potential. Undigested enteral inputs are available to the resident bacteria and the production of metabolites can influence health and nutrition. The preterm pig represents a relevant and translational animal model for understanding GI development and for identifying diet and regulatory factors that stimulate GI growth and maturation after preterm birth and thereby accelerate the transition from parenteral nutrition to full enteral nutrition.