Selection Index to Improve Crossbred Sheep Crossbred lambs sired by high - index Bluefaced Leicester rams grow quicker and have higher carcass quality. That is an important finding of a major research project - the 'Longwool Project' - focused on developing a selection index to improve carcass merit in the crossing sire breeds without compromising their good mothering ability, litter size or hardiness. The Longwool Project started in 1997 with funding from MAFF (now Defra) and MLC (now the devolved bodies of EBLEX, HCC and QMS), and involves the Scottish Agricultural College (Edinburgh), the Institute of Rural Sciences (Aberystwyth) and ADAS (at Rosemaund and Pwllpeiran). Over three years, a total of 1500 Scottish Blackface and Hardy Speckled Face ewes were mated to 45 performance-recorded Bluefaced Leicester ram lambs, which were selected from within the Penglas Bluefaced Leicester Group Breeding Scheme. Around 2200 Mule wethers were slaughtered to provide detailed growth and carcass data, while 1800 Mule ewes were distributed over three sites in Scotland (SAC Edinburgh), England (ADAS Rosemaund) and Wales (IRS Aberystwyth) where they are currently being evaluated for their maternal performance and hardiness over a number of reproductive cycles. To complement the main project, an additional demonstration project was set up at Newton Rigg College in 1998. This has involved Swaledale ewes bred to high index Bluefaced Leicester rams with the performance of their North of England Mule lambs monitored through marketing (wethers) or as breeding females. This has provided a valuable bolt-on to the main project and has allowed demonstration of the project results at a number of sheep events in the North of England, as well as at farm Open Days in conjunction with the Northern Uplands Sheep Strategy to promote genetic improvement in crossing sire sheep. At the start of the project, a preliminary Crossing Sire index was designed for use in the Penglas Bluefaced Leicester Group Breeding Scheme. Since then, the average index value of the purebred lambs born within the scheme has steadily increased each year. Significant genetic progress has been made in muscle thickness but without excess fatness, and, in line with the design of the index, only modest increases in growth rate and mature size. The index value of individual Bluefaced Leicester sires was also positively related to the performance of their crossbred progeny. Mule wether lambs sired by high-index Bluefaced Leicester rams had greater muscle depths and lower fat depths at finished condition. They also had more lean and less fat in every joint when assessed through carcass dissection, with no significant change in carcass weight. The Mule ewes kept for breeding have now produced between 3 and 5 lamb crops, and early indications are that differences between grand-offspring of high- and low-index Bluefaced Leicester rams are in the same direction (although obviously smaller) as for the Mule wethers. These Mule ewes are being retained for a further two years to provide a robust assessment of their productivity, including their longevity. Improvements to the preliminary Crossing Sire index are underway. It is essential that all traits defining the economic worth of a Mule/Halfbred ewe, such as her mothering ability, litter size and hardiness, are ultimately incorporated into the index. An updated index that includes greater focus on the maternal merit and size of the crossbred ewe has been formulated and is being considered for implementation by the Penglas Scheme, and in due course by Bluefaced Leicester breeders in general. Inevitably, the Crossing Sire index will undergo further revision as more information on the relationships between reproductive, growth and carcass traits are collected within the project. In future, inclusion of additional traits like ewe longevity and disease resistance is anticipated, to more comprehensively reflect the economic performance of the Mule/Halfbred ewe. Still, the results to date clearly show the positive effect of index selection within the crossing sire breeds on improving carcass merit. Importantly, even greater opportunities lie ahead. As the index evolves to include the full range of traits important in crossbred ewes, it will prove a central tool to make effective genetic improvement in crossing sire sheep that benefits the entire stratified UK sheep industry. Mervyn Davies ADAS Rosemaund 22 October 2004