Hypoxia and Oxidative Stress Are Associated with Reduced Fetal Growth in Twin and Undernourished Sheep Pregnancies

Abstract

Simple SummaryTwin gestations in sheep are economically more important than single ones; however, twins are born with lower weight, resulting in higher mortality and lower postnatal growth. Chilean Patagonia is very important for sheep production, but its harsh environment results in low food availability and cold and windy conditions during gestation and lambing periods, with a consequent great mortality of twins (~40%). We postulate that the restriction of fetal growth in twin and undernourished sheep pregnancies is associated with fetal hypoxia and oxidative stress. To prove this, single- and twin-bearing ewes were maintained under Patagonian field conditions and offered only natural pasture (undernourished) or natural pasture plus concentrate supplementation (well nourished). Near term, blood gases and oxidative status were evaluated in cord blood, and fetal biometric traits and placental weight were obtained after cesarean section. Both maternal undernutrition and twinning led to decreased oxygen supply to the fetuses, which was associated with decreased intrauterine growth. Moreover, twinning increased oxidative stress at the feto-placental unit, which might also contribute to the restriction of fetal growth. These results highlight the importance of maternal nutrition, especially for those ewes bearing multiples, and opens new possibilities for nutritional or antioxidant interventions for preventing fetal hypoxia and oxidative stress.AbstractLow birth weight has profound implications for perinatal mortality and morbidity in lambs, causing higher mortality and lower growth potential. Low birth weight, as a consequence of fetal growth restriction, occurs in undernourished and multiple pregnancies, where hypoxia and oxidative stress could play a critical role. Our aim was to establish the effects of nutritional deprivation and pregnancy rank on fetal growth, oxygenation, and oxidative status in sheep pregnancies under extensive Patagonian conditions. At 30 days after mating, single- and twin-bearing ewes were offered only natural pasture (undernutrition group) or natural pasture plus concentrate supplementation (well-nourished group). At day 140 of gestation, blood gases and redox status were evaluated in venous cord blood, and fetal biometric characteristics were obtained after cesarean section. Both maternal undernutrition and twinning led to decreased oxygen supply to the fetuses (p = 0.016 and p = 0.050, respectively), which was associated with decreased intrauterine growth (r = 0.446, p < 0.01). Moreover, twinning increased oxidative stress in cord blood (p < 0.05), which might also contribute to fetal growth restriction. These results reinforce the importance of maternal nutrition, especially for those ewes bearing multiples, and opens new possibilities for nutritional or antioxidant interventions for preventing fetal hypoxia and oxidative stress.

Supplementation of Underfed Twin-Bearing Ewes with Herbal Vitamins C and E: Impacts on Birth Weight, Postnatal Growth, and Pre-Weaning Survival of the Lambs

“…In the present experiment, such patterns were clearly observed in sheep supplemented with concentrate but not in non-supplemented ewes, in which BW showed non-significant changes and BCS was always decreasing throughout pregnancy. This finding supports evidence that twin-bearing ewes kept in a natural Magellan Patagonian prairie are normally raised in a state of undernutrition [9].…”

“…Assessment of TAC in newborn lamb plasma was performed using a colorimetric Antioxidant Assay Kit (Cayman Chemical Company, Ann Arbor, MI, USA), previously used for ovine plasma [9,11,14] according to the instructions of the manufacturer.…”

“…All these factors lead to poor water supply in the prairies and therefore limited pasture and nutrient availability [8]. This reduced nutrient availability is especially concerning during pregnancy, resulting in a null body weight increase and around a 22% decrease in body condition score in twin-bearing ewes [9].…”

“…The increase of twin-bearing ewes in the herd is assumed to be a good strategy to improve the productivity of sheep systems, since the additional newborn has a lower energy cost than the maintenance energy of an additional sheep. However, undernutrition of twin-bearing sheep may cause intrauterine growth restriction (IUGR), and therefore low birth weight (LBW) neonates, which suffer from increased morbidity and mortality [9]. In this case, under adverse climatologic and/or nutritional conditions like in the Magellan Patagonia, twin newborn mortality could reach up to 40% [10], negatively impacting profitability and animal welfare.…”

“…We recently demonstrated that IUGR in twin sheep fetuses is associated with hypoxia and oxidative stress [9]. Maternal oral supplementation with vitamins C and E during the pregnancy period (days 30 to 140 of gestation) increases these vitamins in the cord blood of near-to-term fetuses, diminishing the oxidative stress and increasing fetal weight [11].…”