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Beyond the Bale : Apr 07 - May 07
Sire comparison program update Embracing industry initiatives has meant new information is included in Merino Superior Sires (MSS) 12, which has just been released, providing the wool industry with a reliable tool with which to compare the performance of sires. The latest publication has adopted the new common language for describing breeding values. Previously MSSBVs (Merino Superior Sires Breeding Values) were used to compare sires, but sires are now compared using Australian Sheep Breeding Values (ASBVs), which have been generated using all Merino data from Sheep Genetics Australia (SGA). Featuring data from individually recorded Merino flocks, MSS sires are also now directly comparable with Merino data reported by SGA. Anne Ramsay, AWI's project manager for sheep breeding genetics, says that in most cases, the results in this edition of MSS 12 have greater accuracy than previous editions, due to the increased amount of information known about some sires. "The SGA-based analysis is able to account for the wide variety of environments in which Merino sheep are managed across Australia and the wide variation of genetic performance of Merino sheep," she says. "In this report, ASBVs are reported for each measured trait.As each sire or dam only passes half their genes to their progeny, the difference in progeny for a particular trait will be half the value of the ASBV." ASBVs are complemented by visual classing summaries, with the number of tops and culls generated by each sire reported. A summary of conformation and wool quality performance is also available. "The indexes reported differ from those used in the past and have been selected by the Australian Merino Sire Evaluation Association executive to reflect current breeding directions in the Merino industry," Ms Ramsay says. In order to make MSS more applicable, only sires that have entered the sire evaluation since 2000 will be listed in the printed document.The performance of older sires will remain available via the MSS website. ú More information: Merino Superior Sires is distributed to all registered ram breeders and is available free of charge by calling the AWI Helpline on 1800 070 099.To view a more in-depth version of MSS go to http://mss.csiro.au By Gio Braidotti While all sheep inherit the same basic genome, with a similar complement of genes, small variations at specific sites along the DNA strand can account for differences between animals in the performance of a particular trait. By identifying this variation, DNA markers allow breeders to track desired genetic differences and make earlier selection decisions in flocks. Markers alone will not be a 'silver bullet' for achieving breeding objectives. Nonetheless, marker-assisted selection can accelerate genetic gain, and access to the technology is set to improve as markers become commercially available. In addition to DNA tests for parentage, Inverdale® and Booroola (reproduction), MyoMAX®, LoinMAX® (muscling) and i-SCAN® (blindness) markers are available to the sheep industry, and more will be released for commercial use in the next two to five years. Since markers can readily detect genetic merit in an animal as soon as it is born, the technology is especially useful for predicting traits that: ú are difficult or expensive to measure, such as parasite resistance, staple strength, feed utilisation or footrot resistance; ú require the animal's slaughter to measure characteristics such as meat yield and eating quality; ú are not expressed until adulthood, such as reproductive performance; ú are expressed only in one sex, such as milking ability; or ú are detrimental or require special management in homozygotes, such as spider lamb, dark fibres or the Inverdale® gene. SheepGenomics program director Dr Rob Forage says using the markers simply involves taking a blood sample -- typically on a blood card -- and having it analysed by an accredited laboratory. However, he stresses that selection based on a single DNA marker, without reference to other performance characteristics, will not necessarily lead to improved performance. Often it is necessary to take into account complex interactions with other genes that affect a trait. This extra information can be provided by selection indexes or breeding DNA to become a commercial breeding tool DNA markers capable of accelerating genetic progress are becoming commercially available, offering breeders a powerful new tool 10 GENETICS BEYOND THE BALE values (BVs), such as those reported by Sheep Genetics Australia (SGA). "In some cases the advantage of markers is to improve the accuracy of currently available BVs," Dr Forage says. "The marker test is not a replacement or substitute for the ASBV." Australian Sheep Breeding Values (ASBVs) that take marker and phenotype information into account will provide a level of accuracy above those generated using conventional measurement techniques. Only when the DNA marker is for a gene that accounts for the majority of the variation in a particular trait is the ASBV of less use as a selection tool. These markers are called 'major markers'. However, many traits do not have ASBVs, either because they are expensive or impractical to measure in the living animal or on-farm. In this case, the traits may be measured in research flocks and the DNA markers arising through scientific discovery can be used later in commercial flocks as indicators of performance. These are termed 'proxy markers'. Some markers are not yet associated with observable traits, but can still be used to provide parentage information and increase the rate of genetic gain through more precise breeding decisions. These are described as 'utility markers'. SGA manager Dr Alex Ball is working closely with SheepGenomics and marker test providers to gain access to all DNA marker information, which will enable accurate calculation of ASBVs. "SGA is developing its database to ensure that all DNA marker information can be uploaded and, where available, Type I performance markers will be integrated into existing ASBVs," Dr Ball says. "Breeders and producers will get the best value out of markers when they are properly validated and all the information is included in the ASBV calculations." SGA is planning a series of Ram Breeder workshops in 2007 that will include a simple, practical explanation of the principles of markers and how they are being incorporated into ASBVs. ú More information: Dr Rob Forage, 02 9463 9169, firstname.lastname@example.org, www.sheepgenomics.com; Dr Alex Ball, 02 6773 2948, email@example.com; Dr Troy Fischer, AWI program manager sheep productivity, 02 8295 3151, firstname.lastname@example.org Sires are compared using Australian Sheep Breeding Values in the new Merino Superior Sires. PHOTO: DAVE RANKINE 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.
Jun 07 - Jul 07
Feb 07 - Mar 07 Supplement