Livestock Update, March 2003
Scott P. Greiner, Extension Animal Scientist, Beef, VA Tech
EPDs have proven to be the most effective tools for genetic improvement of beef cattle. Since the majority of the genetic progress within a herd is a direct result of sire selection, EPDs should be given careful attention when choosing bulls. With the vast number of EPDs that are available for use, selection goals must be carefully established to determine which EPDs are of primary importance. Additionally, EPDs should be combined with other selection criteria, such as structural and reproductive soundness (for which EPDs are not available), to determine which sires are most suitable.
Once selection criteria have been established (ie. what traits do we need to improve?), benchmarks or an acceptable range of EPDs should be established for application to bull-buying . For example, if the goal is to increase weaning weight of the calf crop, WW EPD would be defined as a primary EPD selection criteria for a new bull. The questions becomes: What WW EPD does the bull ideally need to have? Is there a minimum? or maximum? The likely correct answer is that there is a range in EPDs that would be considered acceptable. The adage that more is better is not applicable in many bull selection scenarios when it comes to EPDs. Higher WW EPDs would certainly achieve the goal of enhancing weaning weights; however, there may also be correlated reductions in calving ease due to higher birth weights or potential increases in mature cow size for heifers retained as replacements. Balanced trait selection is always important. Defining an optimum EPD range or benchmark allows
Defining the optimum EPD range or benchmark, however, can be challenging. Knowledge of the EPD value of former and current sires in the herd can provide valuable insight and assistance in this matter. Associating EPD values on current/former sires with the performance of their progeny can be useful to establish a benchmark from which to select future sires. In the previous example, where enhanced weaning weights was our goal, it would be advantageous to know the WW EPD values of our current sires. We could then set our WW EPD goal at some higher level compared to those bulls. Similar examples can be applied to milk, birth weight, and carcass traits. The basic premise is that defining where we are headed genetically is much easier if we can characterize where we have been.
Breed percentile rankings are additional tools that can assist with EPD selection. It is useful to understand where a particular bull ranks within a breed for traits of interest. This ranking will give a general idea as to the genetic merit of the bull compared to others within the breed. Percentile rankings are readily available in sire summaries published by breed associations. With this information, bulls can be specifically evaluated as to where their EPDs rank in the breed (breed average, top 10% vs. bottom 20%, etc.). It important to note that percentile rankings do not reflect genetic differences for traits between breeds, and can be misleading if not used in the proper context. For example, Simmental and Gelbvieh bulls with milk EPD values that rank relatively low within breed should not necessarily be discriminated against, since the average genetic merit for milk production in these breeds is high. Therefore, the general merit of the breed for each trait needs to be considered along with the rank of an individual bull within that breed.
In summary, EPDs are a powerful selection tool. For most effective use, optimum or acceptable EPD ranges need to be defined and applied to bull selection.