Current Trends in Beef Cattle Genetic Evaluation

Genomic selection has become a reality for the majority of beef cattle breeds that publish Expected Progeny Differences (EPD). Until recently, all beef breed associations augmented traditional EPD with genomic predictors in a two-step fashion. The first step included estimating marker effects through a training and evaluation process by which a resulting genomic prediction equation was generated and then applied to subsequently genotyped animals. The resulting genomic predictor was included in genetic evaluations either through a correlated trait approach or through an index-based approach. In either case, there is evidence that resulting genomic-enhanced EPD (GE-EPD) were biased and thus the two-step procedures were suboptimal. Newer, ‘single-step’, approaches seek to reduce this bias by incorporating maker data in a simultaneous fashion with available pedigree and performance data in genetic evaluations. The American Angus association made this change in July of 2017, and the majority of other beef breeds are in the process of moving in this direction and will likely have done so by the time of this meeting. There are two competing models and thus software platforms available to perform a ‘single-step’ evaluation; single-step genomic BLUP (ssGBLUP) and the super hybrid model. A key difference between these models is the assumption of differential marker effect sizes. As currently implemented by Angus Genetics, Inc., the ssGBLUP model assumes all markers have the same effect on a given trait while the super hybrid model was proposed as a means of allowing some markers to have larger effects than others for a given trait. Breed organizations currently in the testing stage of the super hybrid model include the American Hereford Association and the breed associations participating in the International Genetic Solutions consortium. Genetic evaluations have never been static and these changes are part of a much-needed evolution in genetic evaluation procedures. Unfortunately, the early, and in many cases premature, commercialization of genomic tests prior to GE-EPD has led to considerable confusion and angst among beef cattle producers as genetic evaluation systems evolved to accommodate this new source of data. Consequently, the objectives of this abstract are to detail the changes in genetic evaluations of beef cattle as they relate to genomic selection and to provide comment relative to the researchable questions that still exist as genetic evaluations continue to evolve.