Lamb survival – balancing genetics, selection and management

The historically small size of the Australian sheep flock, along with the relatively high sheep and lamb prices compared to wool returns, has highlighted the issue of low reproductive efficiency of the Australian sheep flock, particularly the Merino. The major obstacle to improving net reproduction rate (NRR, the number of lambs weaned per ewe joined) is lamb survival. The animal welfare issues relating to lamb survival are discussed along with the major causes of lamb loss and factors that impact on lamb survival. The successful rearing of a lamb to weaning is the culmination of a sequence of often interrelated events involving genetics, physiology, behaviour and nutrition, with the environment providing an overarching complication. These interacting factors affect the outcome of an individual pregnancy, while the success or failure of each individual pregnancy determines the overall reproductive success of the whole flock. Three options are available for commercial sheep producers to improve reproductive efficiency. Firstly, Australian Sheep Breeding Values (ASBVs) can be used to select rams whose daughters will wean a higher percentage of lambs leading to improvements in lamb survival in future generations. Secondly, a combination of identifying and retaining the best performing ewes on the basis of NRR and removing the worst performers from the flock will improve lamb survival in the current generation. Thirdly, management options that involve monitoring and actively managing ewe nutrition during pregnancy and optimise the features of a lambing paddock will help boost lamb survival. Actively managing the body condition of the ewes during pregnancy to a target fat (or condition score) of 3 can significantly improve lamb survival, particularly that of twins. Minimising the impact of chill within the lambing paddock through reducing wind speed, increasing temperature and reducing dampness will enhance lamb survival. The benefits of each of these three options are cumulative, such that improvements in NRR of 14% within 10 years are possible. However, prior to the development of extension programs endorsing these three strategies to improve lamb survival, they must be demonstrated in commercial flocks across a range of production environments and proven to work over a number of seasons.