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

Simple Summary Twin 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 (similar to 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. Abstract Low 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.