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Centre for Genetic
Improvement of Livestock Honing In On Genes
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To strengthen
genetic improvement programs for Canadian Holsteins, University of Guelph
researchers are collaborating with Western Canadian colleagues to detect
Holstein genes that have economically important effects on traits such as
milk production.
Prof. John Gibson and recent Ph.D. graduate Jeya Nadesalingam, Centre for Genetic Improvement of Livestock, along with Yves Plante, Bovine Blood Testing Laboratory, Saskatchewan, are working on an extensive study to understand the genes that cause variation in dairy cattle. Pinpointing the source of variation in animals is the key to making genetic improvements. The project, a combination of molecular genetics and quantitative statistics, will help increase the rate of genetic improvement in Canadian Holsteins and potentially reduce the cost of current bull testing programs. The study started in the fall of 1996, and looks at the genetics of six prominent Holstein bulls. The researchers are following the inheritance of special genes -- known as quantitative trait loci or QTL-- in 70 sons of each bull. These QTLs are segments of DNA that, if inherited by a calf, will lead to an improvement in a certain trait, such as milk production. The tools that allow researchers to explore and track the inheritance of QTL are called genetic markers. Genetic markers act like bookmarks; they're tiny fragments of DNA that are unique to Holstein cattle. Each marker is a landmark at a specific point on a particular chromosome. So, when researchers follow the inheritance of a particular marker from parent to offspring, they also follow the inheritance of a particular region of a chromosome. Using genetic markers called microsatellite markers, the researchers genotyped the sons of six popular bulls and used the marker genotype information to determine which copy of each chromosome segment was inherited from the sire. They then related that information to the genetic value of each son to determine which, if any, segments had useful effects on milk production. After performing and analyzing more than 20,000 genetic tests, the data has shown that several QTL have substantial effects on Holstein milk production. Given that QTL exist, it is now possible to use genetic markers to track the inheritance of QTL in new sons or grandsons. Sons that inherit desirable QTL are much more likely to be useful in genetic improvement programs than average sons. Sons that don't inherit useful QTL have little chance of scoring high in the standard progeny test that every bull must go through. Because progeny testing is expensive - about $50,000 per bull -- cattle breeders can reduce costs by only testing those animals that have the greatest chance for success. Continued Expansion Gibson says the project analysis will continue to expand. He and his colleagues plan to search for genes controlling additional traits, such as somatic cell counts, milking speed, temperament and 40 different conformational traits, including feet and legs and udder conformation. The researchers hope industry will take these results to heart and pursue studies to confirm existing QTL, to locate QTL more accurately, hunt for a wider range of QTL and ultimately put these techniques into routine application in their breeding programs. The research is sponsored by DairyGen (formerly the Cattle Breeders' Research Council), the National Research Council IRAP program, the Natural Sciences and Engineering Research Council and the Ontario Ministry of Agriculture, Food and Rural Affairs. |
