Fetal mortality from day 30 of pregnancy in Merino ewes offered different levels of nutrition

The effect of nutritional restriction during mid pregnancy on fetal mortality was examined in 3 experiments in which multiparous 3-6 year old Merino ewes were fed at maintenance (M) or 0.3M from about day 30 to 90 of pregnancy, followed by M or 2M for the remainder of gestation. Fetal wellbeing was determined by ultrasound examination at periodic intervals throughout pregnancy. Among 134 single borne fetuses, mortality was detected in only 3, between days 70-92 of pregnancy. There were no losses in 58 ewes bearing twins and fed at M. By comparison, 9 of 93 ewes bearing twins and fed at 0.3M lost 1 or both fetuses between days 30 and 95, and a further 3 of 66 remaining ewes had fetal losses between days 95 and 140. It was concluded that such losses in ewes bearing twins during periods of nutritional restriction may need to be considered when using scanning to predict the number of lambs born. Also it highlights the need to confirm the viability of each fetus during ultrasound examinations of multiple fetuses.