Expected Progeny Differences have proven to be the most effective tool for genetic improvement of beef cattle. The majority of the genetic progress within a beef herd is accomplished through sire selection, and therefore EPDs play a primary role in identifying and purchasing bulls. Advancements in science and technology have resulted in a large number of EPDs being developed for multiple traits. Producers are faced with two particular challenges as a result: 1) Which EPDs should I focus my selection on? and 2) What should be the target value of the EPDs of importance?
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 become: What WW EPD does the bull ideally need to have? Is there a minimum? or maximum? In most situations, there is likely a range in EPD values that would be considered optimum. The adage that “more is better” is often not applicable in most 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 and defining an optimum EPD range as a benchmark is compatible with this strategy.
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 a goal, it would be advantageous to know the WW EPD values of current sires. We could then set our WW EPD goal accordingly higher. Similar examples can be applied to milk, calving ease, 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 relative to all animals in the breed for specific traits. The following table provides a brief summary of percentile rankings in Angus and Purebred Simmental bulls for calving ease, yearling weight, milk, and marbling EPDs. It important to note that percentile rankings do not reflect genetic differences for traits between breeds, and can be utilized on a within-breed basis. Utilizing the percentile table, it can be determined that an Angus bull with a Calving Ease EPD of +8 or higher ranks in the upper 25% of the breed for calving ease, and would be a strong candidate for use on heifers. Similarly, a Simmental bull with a milk EPD of +5 is slightly higher than the Simmental breed average for milk. These percentile rankings also illustrate practical differences between EPDs. In other words, differences of a couple of pounds of WW or YW EPD between bulls are rather insignificant in the grand scheme of selection, as examination of the percentile rankings for these differences reveal that these bulls would essentially rank identically within the breed. A two pound difference in birth weight, however, is a substantial difference.
Percentile Rankings for Angus and Purebred Simmental Bulls
|50% (breed avg)||+6||+84||+22||+.33||+7||+56||+4||+.13|
In summary, EPDs are a powerful selection tool and establishment of herd goals and benchmarks are important for optimal utilization. Tracking performance of progeny and percentile ranks are two mechanisms that assist in the establishment of benchmarks to be applied to bull-buying decisions.
Virginia Cooperative Extension materials are available for public use, re-print, or citation without further permission, provided the use includes credit to the author and to Virginia Cooperative Extension, Virginia Tech, and Virginia State University.
Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Alan L. Grant, Dean, College of Agriculture and Life Sciences; Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Jewel E. Hairston, Administrator, 1890 Extension Program, Virginia State, Petersburg.
January 27, 2011