BOARD-INVITED REVIEW: Intrauterine growth retardation: Implications for the animal sciences1

Abstract

Intrauterine growth retardation (IUGR), defined as impaired growth and development of the mammalian embryo/fetus or its organs during pregnancy, is a major concern in domestic animal production. Fetal growth restriction reduces neonatal survival, has a permanent stunting effect on postnatal growth and the efficiency of feed/forage utilization in offspring, negatively affects whole body composition and meat quality, and impairs long-term health and athletic performance. Knowledge of the underlying mechanisms has important implications for the prevention of IUGR and is crucial for enhancing the efficiency of livestock production and animal health. Fetal growth within the uterus is a complex biological event influenced by genetic, epigenetic, and environmental factors, as well as maternal maturity. These factors impact on the size and functional capacity of the placenta, uteroplacental blood flows, transfer of nutrients and oxygen from mother to fetus, conceptus nutrient availability, the endocrine milieu, and metabolic pathways. Alterations in fetal nutrition and endocrine status may result in developmental adaptations that permanently change the structure, physiology, metabolism, and postnatal growth of the offspring. Impaired placental syntheses of nitric oxide (a major vasodilator and angiogenic factor) and polyamines (key regulators of DNA and protein synthesis) may provide a unified explanation for the etiology of IUGR in response to maternal undernutrition and overnutrition. There is growing evidence that maternal nutritional status can alter the epigenetic state (stable alterations of gene expression through DNA methylation and histone modifications) of the fetal genome. This may provide a molecular mechanism for the role of maternal nutrition on fetal programming and genomic imprinting. Innovative interdisciplinary research in the areas of nutrition, reproductive physiology, and vascular biology will play an important role in designing the next generation of nutrient-balanced gestation diets and developing new tools for livestock management that will enhance the efficiency of animal production and improve animal well being.

Effects of maternal nutrition on the expression of genomic imprinted genes in ovine fetuses

“…Alternatively, the practice of flushing before and during the breeding season can result in overfeeding [50]. Such nutrient imbalance has been shown to severely impair fetal and placental development [50]. Interestingly, we found most of the disturbed gene expression were located in the KCNQ1 and IGF2/H19 clusters, consistent with the role of IGF2 as a major fetal growth regulator [54].…”

“…Maternal stressors induce changes in expression of the fetal genome, which can permanently alter the offspring’s physiology, development, metabolism, and growth [50], as reported in mice and rats [51,52]. Understanding the effect of poor maternal nutrition in ovine fetal development is not only relevant to agriculture [53], but also to modeling for human pregnancy and fetal development.…”

“…Nevertheless, during late gestation, when fetal growth is the most rapid, food becomes scarce, leading to nutrition restriction. Alternatively, the practice of flushing before and during the breeding season can result in overfeeding [50]. Such nutrient imbalance has been shown to severely impair fetal and placental development [50].…”

Consequences of a low litter birth weight phenotype for postnatal lean growth performance and neonatal testicular morphology in the pig

“…Even within a normal birth -E-mail: mnsmit@ualberta.ca weight (BW) litter, intrauterine growth restriction (IUGR) and a low birth weight (LBW) can be characteristics of individual pigs (Wu et al, 2006). However, other studies suggested that IUGR can be a litter characteristic, driven by high ovulation rates and good to moderate early embryonic survival to day 30 of gestation in higher parity sows (Vonnahme et al, 2002).…”

Nutrient-intake-level-dependent regulation of intestinal development in newborn intrauterine growth-restricted piglets via glucagon-like peptide-2

“…Neonates born with IUGR have increased risk of postnatal morbidity and mortality, and IUGR is considered to be a major health concern worldwide for both humans and commercially raised domestic animals (Bateson et al, 2004;Wu et al, 2006). IUGR has been primarily attributed to placental insufficiency during the intrauterine phase (Wu et al, 2006), and can be regarded as the failure of a fetus to reach its genetic growth potential.…”