Submitted to: Journal of Animal Science
Publication Type: Review Article
Publication Acceptance Date: April 9, 2001
Publication Date: November 1, 2001
Citation: Sonstegard, T.S., Van Tassell, C.P., Ashwell, M.S. 2001. Dairy cattle genomics:tools to accelerate genetic improvement. Journal of Animal Science. 79:E307-E315.
Traditional selection based on genetic merit calculated from phenotypic and pedigree information has been tremendously effective at improving production in dairy cattle. Hypothetically, genetic improvement could be accelerated even further for yield and other economically important traits by directly selecting upon the genetic differences underlying the phenotypes. To elucidate these genetic differences, we have developed a research strategy based on genomics to identify economic trait loci (ETL).Then DNA marker based tests developed for these ETL can be practically applied to enhance selection in a commercial setting. Initially, ETL have been detected in a US Holstein grandsire family using the granddaughter design and analysis of variance. Further genotypic analysis for two of these ETL have reliably identified milk and dairy form ETL on Chromosomes 6 and 27, respectively. Because the marker intervals identifying these ETL are not resolved well enough for accurate selection in current populations, we expanded the depth of our analyses to include an ongoing collection of animals from extended pedigrees. Increasing genotypic and phenotypic information alleviates the statistical limitations of ETL interval refinement inherent in the historic experimental population in two ways. First, the population size is not limited or biased by previous selection. In addition, the inheritance of ETL will be traced from historic families of interest to current generations relevant to the industry. After allele frequency and contribution to phenotype are determined in current populations, those ETL most beneficial for the industry can be accurately used for selection. Genes expressed in the mammary gland will also be mapped and characterized to increase gene marker density near ETL.