Carcass EPDs are evaluated at an age constant endpoint, which means that the ribeye area (REA) EPD is expressed at a constant age. However, in the real world, REA at a constant age has no pratical application. What is important is REA relative to carcass weight, which is how the Yield Grade (YG) formula works and how value is determined. Expressing REA EPDs at a constant age leads to various biases, for example, high growth, but light muscled cattle can, and often do, have positive REA EPDs.
In 1999 I expressed concern to the American Angus Association (AAA) that the bias in the age constant endpoint would result in REA EPDs that are flawed and misleading for real world applications. Now, it's ten years later, and the trends established are clear and predictably disturbing--REA EPDs are increasing year over year (in 1995, the average REA EPD was -.05, in 2008 the average REA EPD was +.17) while the kill data show that REA relative to carcass weight is decreasing. Some back of the envelope calculations follow to supoort this claim.
For steers harvested between 360 to 480 days of age, the Fall 1999 Sire Evaluation shows about 30,000 steers in the database with an average carcass weight of 762 pounds and an average REA of 12.43 square inches. The YG formula shows that a 762 pound carcass needs 12.95 square inches of REA to be "average", so this age group of cattle in the database in 1999 were .52 square inches below average.
Similarly, for steers harvested between 360 to 480 days of age, the Fall 2009 Sire Evaluation shows nearly 58,000 steers in the database with an average carcass weight of 779 pounds and an average REA of 12.47 square inches. When the 30,000 steers included in the 1999 database are removed from consideration, the approximately 28,000 steers placed in the database between 1999 and 2009 should have an average carcass weight of 797 pounds and an average REA of 12.51 square inches. The YG formula shows that a 797 pound carcass needs 13.36 square inches of REA to be "average", so the steers that entered the database between 1999 and 2009 are .85 square inches below "average".
In the last 10 years, the REA EPD has increased significantly (.2 square inches), while the kill data show that REA has actually decreased by .33 square inches on a carcass weight basis. In order for REA EPDs to be meaningful, it should be clear that we need something better than the current REA EPDs. We need a REA EPD that is expressed relative to carcass weight, preferably using the YG formula as the standard for evaluation.
The USDA Quality Grades establish the standard for the increments used in both marbling evaluation and marbling EPDs. Likewise, the YG formula should be established as the standard for the evaluation of REA EPDs.
Under this proposed scenario, consider the following example. Two bulls, A and B, with progeny evaluated at an age constant endpoint, each have an average progeny REA of 13.1 square inches. (Under the curent system, their REA EPDs would be the same.) However, Bull A's progeny have an average carcass weight of 800 pounds while Bull B's progeny have an average carcass weight of 750 pounds. According to the YG formula, an 800 pound carcass needs 13.4 square inches of REA to be average, while a 750 pound carcass needs 12.8 square inches to be average. Under the new proposal, Bull A would have a REA EPD of
-.30 (13.1 - 13.4) while Bull B would have a REA EPD of +.30 (13.1 - 12.8).
It should be a fairly straightforward exercise to analyse the data to create REA EPDs as suggested to determine if these EPDs more accurately describe the trend expressed in the kill data. It may be necessary to evaluate the data with various endpoints (age, backfat, carcass weight) to discover which endpoint most accurately describes the data when REA EPDs are expressed relative to the YG formula.
I have shared these concerns once again with the AAA. One lonely voice will not be enough to cause change. If you agree that REA EPD evaluation needs to be examined, and likely changed, then please pass the word. Perhaps the collective voice of the AAA membership can have success with staff and directors to facilitate change.
Bobby Grove
White Ridge Angus