Use of Genetic Marker Information in Cattle Selection
by Troy Smith, field editor
DES MOINES, Iowa (Sept. 8, 2016) — Geneticist Alison Van Eenennaam made one thing perfectly clear. “Genomics,” she said, “is not a silver bullet. It is not a replacer, but a helper.”
A University of California–Davis Extension specialist in animal genomics and biotechnology, Van Eenennaam discussed the role of genomics in breeding selection during the Applied Reproductive Strategies in Beef Cattle symposium Sept. 7-8 in Des Moines, Iowa. Van Eenennaam said DNA testing of cattle holds much potential for more extensive use in genetic selection, but it also has been the subject of considerable hype.
DNA testing is performed to determine whether animals carry genetic markers — certain differences in gene sequence associated with specific characteristics or traits. Van Eenennaam said DNA testing can be used for a variety of purposes such as pedigree verification, aiding in selection and breeding choices, sorting cattle into management groups, and marketing based on test results. The simplest application is to determine parentage, such as finding out which bull sired a calf born to a cow that had been exposed to multiple bulls.
“The real power of genomics is in the ability to test for carriers of genetic traits,” added Van Eenennaam.
She explained that genomic testing is available through breed associations who have partnered with two companies (Zoetis and Neogen GeneSeek) that provide genotyping services. There are several types of tests which differ mainly by the number of genetic markers included. The so-called high-density chips have somewhere between 50,000-150,000 single nucleotide polymorphism (SNP) markers on a single assay. For less cost, lower-density chips can be used for “imputation” up to the high-density chip.
According to Van Eenennaam, soon after the first genetic tests were released, efforts began to incorporate DNA information into genetic evaluations conducted by breed associations — the goal being to increase the accuracy of prediction for genetic merit. Rather than replacing expected progeny difference (EPD) values as selection tools, the incorporation of genomic information results in genomically enhanced EPDs with improved accuracy.
Van Eenennaam said breed associations must test the predictive power of genetic tests for traits of interest, using large “training” populations for which phenotypic data has been collected.
“Genomics is all the more reason that we need phenotypes,” stated Van Eenennaam.
Reminding her audience that many economically important traits of beef cattle are influenced by hundreds, even thousands of genes plus the environment, Van Eenennaam said a few gene markers cannot sufficiently account for much additive genetic variation. Consequently, the value of DNA testing currently available should not be oversold.
Van Eenennaam also advised commercial cow-calf producers to use caution if they are considering the genetic tests now available for commercial heifers. For some producers, testing may hold little opportunity for economic return. An example would be testing for carcass traits by a producer that sells calves at weaning.
“Be sure the information gained will translate to value that can be captured,” urged Van Eenennaam.
Van Eenennaam spoke during Thursday’s ARSBC session focusing on genetics. Visit the Newsroom at www.appliedreprostrategies.com, which features comprehensive coverage of the symposium, to view his PowerPoint, read the proceedings or listen to the presentation. Compiled by the Angus Media editorial team, the site is made possible through sponsorship by the Beef Reproduction Task Force.
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