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Beyond the Bale : Aug 07 - Sep 07 Supplement
By Kellie Penfold Photo John Owens DNA markers are likely to be the first product in the marketplace as a result of the SheepGenomics program. "Within 12 months we expect to have a research- grade product available," says Dr Rob Forage, SheepGenomics program director. "From there it will be further refined so it is usable and affordable for the livestock industry." SheepGenomics is a $30 million initiative of AWI and Meat and Livestock Australia, with 11 leading research organisations in Australia and New Zealand working to determine gene function from genomic information in sheep and harnessing that information to address industry needs. Dr Forage describes the bulk of the SheepGenomics work as "playing leapfrog" by building on prior investments and technology advances in sequencing the human and cattle genomes. "This allows us to discover DNA markers before sequencing the entire sheep genome, and has saved the industry both time and money," he says. "DNA markers are indicators of genes that influence traits carried by that animal, and that is where production gains stand to be made: hence our focus on that area," Dr Forage says. "In the process, it is helping complete our first glimpse of the sheep genome. Already, through the DNA marker work, we've sequenced about six per cent of the sheep genome and have been able to compare the locations of those fragments with human, cattle and dog genomes. This gives us a good working map, or virtual sheep genome, but a full sequence will take some years and millions of dollars from international collaboration." The beauty of establishing DNA markers is that they will allow a flock to be moved towards its production goal faster. Through a simple blood test soon after birth or at weaning, the genetic traits of the sheep will be known and classing and culling can take place accordingly. Many traits are expensive to measure (for example, staple strength) or difficult to measure (for example, parasite resistance), so once DNA markers are discovered for these traits, selection can be faster and more effective. Another application of DNA markers is for undesirable traits such as dark fibre, where the aim is to eliminate breeding animals carrying these genes. There are four broad classes of DNA markers, each of which provides value, but should be used differently to ensure maximum value (see table below). Dr Forage says the challenge lies in developing a single test platform and correlating the markers with a range of production traits. "The areas we are focusing on are parasite resistance, meat and MARKING OUT NEW GENETIC TERRITORY DNA marker technology -- the fruit of the SheepGenomics program -- could be available to the industry by 2008 wool production and quality and lamb sur vival, as well as looking for some specific genes such as those which indicate carriers of dark fibres. "There will be a large number of traits that will be impractical to measure on the living animal or on-farm during normal management practice. In this case, the effect of the markers will be measured in research or experimental flocks and the results extrapolated to normal commercial flocks. In other cases, if the DNA marker is for a gene that accounts for the majority or 100 per cent of the trait, there is no need to have an ASBV." Dr Forage says that the stud industry will be early adopters of the technology, which will then flow through and affect commercial flocks. "The producers I talk to are really excited by the prospects DNA markers offer them, but my advice is that they are not a silver-bullet solution. "DNA markers should be treated as additional information to assist in good on-farm management for increased production gains. They will allow increased accuracy in predicting performance, but they should not be used on their own. When combined with information from SGA, they will be a very powerful tool." ú More information: www.sheepgenomics.com SHEEPGENOMICS 14 BEYOND THE BALE BREEDING FOR PROFIT SUPPLEMENT The SheepGenomics DNA marker resource flock is run at AWI's Falkiner Memorial Field Station in Deniliquin, NSW. Four types of DNA markers MARKER FUNCTION MARKER TYPE EXAMPLES INTEGRATED INTO ASBVs RATIONALE Performance I -- Integrated Wool quality Yes ASBV already exists for a polygenic trait. The marker adds accuracy to the trait and enables selection to occur at a potentially younger age. Performance II -- Proxy Footrot, other disease-susceptibility and resistance No ASBV is not available in commercial flocks. Marker utility for polygenic traits is measured in research flocks. Performance III -- Major Poll, dark fibre, deleterious recessives, eg spider lamb No Typically a single locus trait for which the marker explains majority (or all) of the trait. Parentage IV -- Utility Parentage testing No Not necessarily associated with a functional gene or obser ved trait but useful for DNA profiling.
Oct 07 - Nov 07
Aug 07 - Sep 07