Sheep Updates 2009

New research is helping to design a Merino ewe for the future that is more robust and has better maternal ability, the work has shown that: • Selection for muscling increases the proportion of twins • Selection for growth also increases the proportion of twins and improves ewe milk production and lamb growth to weaning • Concurrent selection for growth and muscling will have no net effect on lamb birth weight and therefore no increase in lambing difficulties • Genetically fatter ewes provide a better maternal environment for lambs resulting in high lamb birth weight when ewe nutrition is limiting • Selection for high fleece weight can result in higher lamb mortality INTRODUCTION These are challenging yet exciting times for the Australian sheep industry. The industry is under pressure from a changing more variable climate, increased consumer demand for safe and welfare friendly products and the need to run more sheep per person and therefore handle them less often. At the same time there has been a significant change from the traditional dominance of income from wool to a balance between income from wool and meat. All these factors are forcing producers to re-think their sheep enterprises and indeed the type of sheep they are running. While these changes could all seem too much, it is a great opportunity to re-focus our sheep flocks on to a path of profitability within a variable future. METHOD A series of experimens and analyses have been conducted to investigate the impacts of different selection strategies on the reproductive ability of Merino ewes. These experiments and analyses were designed to investigate the independent effects of differences in ewe growth, muscling, fatness and fleece weight genotype on their reproductive capacity. Ewe genotype was determined based on their Australian sheep breeding values (ASBVs) for the traits of interest. Experiments were conducted on 1.5 year old Merino ewes from both Merinotech WA and Billandri flocks. RESULTS The work showed that under high stocking rates or nutrition limited environments, ewes that have higher ASBVs for fatness will produce heavier lambs that have a higher chance of surviving than ewes with lower fatness breeding values. In addition this work showed that ewes with higher muscling ASBVs will produce a higher proportion of twins, lambs with lower birth weight (with no negative impact on survival) and in some circumstances lambs that grow slightly slower to weaning. The work also highlighted that ewes with higher growth ASBVs will produce a higher proportion of twins, produce lambs of higher birth weight, and produce more milk and lambs that grow faster to weaning. Importantly, the work confirmed the previous work of the late Dr Norm Adams and others that selection for increased fleece weight without increasing body weight, results in higher lamb mortality. Ewes with high ASBVs for clean fleece weight had around 10% higher lamb mortality in single born lambs than ewes with average ASBVs for clean fleece weight. CONCLUSION The work suggests that Merino breeders should focus on breeding for a balance between muscling and growth breeding values to maximise improvements in the number of lambs born and also improve lamb growth to weaning. In addition, by selecting for a combination of muscling and growth, the problem of increasing lamb birth weight and potentially lambing difficulties by selecting just for growth will not be apparent as concurrent selection for muscling nullifies this effect. This work has demonstrated that there are a range of impacts of different selection strategies on ewe reproductive performance and these impacts have largely not yet been included when determining the value of selection for particular traits. It is also relatively unknown how the importance of selection for particular traits changes under different production systems or environments. New work under development by DAFWA with support from the Sheep CRC will further investigate the correlation between production traits and maternal performance and importantly determine the impact of various traits on whole farm profit. The new work will investigate how sheep production genetics can be best matched with production systems resulting in greater efficiency and ultimately more robust genotypes that minimise profit variability between seasons.