FEATURE ARTICLE
by Troy Rowan, Ph.D., Assistant Professor and Extension Specialist (Beef Genetics), Departments of Animal Science and UTCVM Large Animal Clinical Science, UTIA Genomics Center for the Advancement of Agriculture, University of Tennessee, Knoxville When we breed cattle, we’ve engaged in the “long game” of genetic progress. Our goal is to make this generation better than the last one. This sustained genetic progress is built on making the right decisions more often than not. By the “right decision,” I mean that the animals (AI sire choice, bull purchase, replacement heifer selection), we are choosing are the animal(s) with the best actual genetic merit for the traits that align with our breeding goal. EPDs are our best tool for ensuring that our selection decisions are “right” more often. Darrell discussed at length in the March issue that EPDs allow us to break an animal’s phenotype into its environmental and genetic components. This allows us to make selection decisions only on our statistical estimate of an animal’s genetic potential. This month, Darrell discusses the concepts of accuracy and possible change, two values associated with an EPD that directly affect selection accuracy. In March’s issue, J.R. Tait described the differences between pedigree and genomic relationships. We know that siblings receive 50% of their DNA from each parent. WHICH 50% they get differs. Anyone with a brother or 40
May 2022
sister (who isn’t an identical twin) knows that significant phenotypic differences (I don’t know about you, but I’m sure better looking than my little brother) can exist between full siblings raised in the same environment. This is a function of what we call Mendelian Sampling, or more simply put, the random sampling of genes. This randomness of passing on of genes from parents to their offspring is why we resemble our relatives but don’t look identical to them. Our goal with EPDs is to estimate which genes an animal inherited from its parents. Typically this has come from information on offspring or relatives (i.e., a bull with larger progeny is likely to have inherited more favorable DNA chunks that control size). The more information on an animal, the more accurate our estimate of that value (and their EPD) will be. Genomics has revolutionized the way that we calculate EPDs and make selection decisions. As Darrell discussed, traditionally, the way that we’ve seen EPD accuracies increase is through the addition of progeny or relative records into the genetic evaluation. This means that for producers who buy young bulls, the limited amount of information makes accuracy relatively low. Genomic tests can increase
