Perinatal lamb mortality – a challenge in extensive sheep enterprises

Perinatal lamb mortality remains a challenge for sheep producers worldwide. Despite considerable research on improving lamb survival, recent surveys in Australia suggest that perinatal lamb mortality levels have remained relatively consistent over the past thirty years. Twin born lambs and lambs from maiden ewes have been identified as the highest at risk, and mismothering- exposure (referred to as starvation, mismothering and exposure (SME)) and dystocia have been consistently identified as the main contributors to perinatal lamb mortality.
Recent efforts to decrease losses have focused on using ultrasound pregnancy diagnosis (scanning) to identify and separate single and multiple bearing ewes in early/ mid pregnancy (day 50-90). Twin bearing ewes are given preferential nutritional management from scanning until lambing in an effort to increase lamb birthweights, and ewe mothering ability. Single bearing ewes are managed to gain less weight to avoid overweight lambs and subsequent dystocia. Paddock selection for lambing is influenced by availability of feed and shelter, with twin bearing ewes generally being allocated to the paddocks with the best shelter.
These management principles, developed as part of the Lifetime Wool research project, have been promoted to producers as part of the Lifetime Ewe Management program, with an estimated 3,800 producers expected to have completed the 12 month program by 2019. This program encourages keeping ewes in better condition score, to produce more lambs and decrease perinatal lamb mortality, and claims to increase weaning percent by 7-8%. However, two surveys, carried out two years apart, of predominantly southern NSW sheep producers who largely adopted these practices, found perinatal lamb mortality rates similar to rates normally expected. Further, the promotion of increased ewe condition at joining is likely to lead to increased numbers of twin bearing ewes. As perinatal lamb losses are 2-3 times greater in twin born lambs, it is likely that even though weaning percentages are increased, actual numbers of lambs dying around birth are also increased. This highlights the difficulties associated with improving weaning rates, especially in Merino sheep and the challenges faced with perinatal lamb mortality.
In an effort to specifically improve lamb survival from maiden ewes, maiden ewes were exposed to lambing adult ewes prior to the maiden ewes lambing, with the expectation that mothering ability may be improved by observing mature ewe bonding behaviour. However, no improvement in lamb survival was apparent following exposure.