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 Carcass EPDs - The Unintended Consequences

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Posts : 70
Join date : 2012-04-16
Location : north central SD

PostSubject: Carcass EPDs - The Unintended Consequences   Mon Mar 11, 2013 4:33 pm

The following letter was given to me by a neighbor a few years back. I'm not sure where he ran across it. I'm not even sure if it was just addressed to him or what. I've been meaning to put it up for some time but just today figured out how to let the computer scan the paper and copy the text. There might be a handful of formatting errors, I was too lazy to proofread the whole thing.

Carcass EPDs-The Unintended Consequences
The EPDs for ribeye area (REA) and marbling are the two most widely used carcass EPDs in the beef industry. Unfortunately, fundamental flaws within each EPD have lead to a myriad of problems relating to their real world usefulness. As currently presented, , these EPDs are often misleading and provide a disservice to the Angus breed and its membership. Fortunately, these fundamental flaws can be corrected-and they need to be corrected-to provide seedstock producers with the tools needed to make real world progress.

More information for marbling exists in the database from ultrasound measurements taken from yearling bulls than from any other source. It has been well documented that testosterone has a strong antagonistic effect on marbling. (Yearling Angus bulls currently average about 3.75% IMF, while estimates for their steer mates show IMF scores between 4.75% and 5.75%, which represents an increase in IMF scores between 26.6% and 53.3%. This increase is solely due to the absence of testosterone in the steers.) That means that two bulls with the identical genetic ability to sire marbling will have dramatically different marbling scores if one has high levels of testosterone and one has low levels of testosterone. Therefore, in our race to improve quality grade, we have likely indirectly selected for low testosterone bulls. Low testosterone bulls might well pass a semen test, but they could also be low libido, low fertility bulls. More open cows and more late calving cows would be the result without any real world concurrent improvement in marbling. (Fertility is the single most important trait for cow-calf producer profitability.) Many breeders believe that selecting for marbling has concurrently caused for selection against early puberty (the early onset of the rise in testosterone), which has negatively affected fertility. We are hearing more anecdotal stories of (1) libido and fertility problems with young Angus bulls, (2) how earlier maturing, high libido bulls consistently score poorly in ultrasound marbling evaluations, and (3) how steers sired by high IMF bulls and low IMF bulls had identical marbling scores at harvest.

To further complicate matters, many breeders are now using DNA marker based information to enhance EPDs. Since most of the data are from yearling bulls and since the markers are simply genetic material that follows a specific trait, the question becomes what percentage of DNA markers for marbling follow low testosterone levels instead of DNA information for marbling? It should be noted that research has never been done to quantify the effects of testosterone on marbling levels. Fundamental research needs to be conducted as soon as possible to determine the exact effect of testosterone on marbling and to eventually adjust the EPDs and DNA markers accordingly. In all likelihood, multiple levels of research need to be investigated, including, but not limited to: (1) a study to measure testosterone levels from weaning to yearling to determine the 2
degree to which early or late puberty affects marbling, (2) a tightly controlled study where blood samples are taken throughout the day from yearling bulls to determine testosterone fluctuations, (3) establishing the relationship between scrotal circumference, testosterone levels, and marbling, and (4) a sire group study whereby blood samples are collected for testosterone analysis when bulls are scanned for ultrasound carcass evaluation.

Some would argue that the EPD for marbling works fine because the CAB acceptance rate has increased the last two years. The improvement in CAB acceptance rate is likely due to a number of factors not related to the marbling EPD, which include the adoption of best management practices to optimize marbling levels and the fact that the influence of Angus genetics is at an all time high in the nation's cowherd. However, the greatest effect on CAB acceptance rate increase is likely the result of the removal of the yield grade requirement for CAB acceptance. The bar for acceptance has been greatly lowered as the yield grade requirement has been replaced with three easily attained criteria---(I) REA between 10 to 16 square inches, (2) hot carcass weight of 1000 pounds or less, and (3) less than 1 inch of backfat. The lack of REA in relation to hot carcass weight prevented many carcasses from being eligible for CAB acceptance when the yield grade requirement was in effect. So instead of improving muscling, AAA elected to remove it from consideration for all practical purposes.

Ribeye Area

The USDA Quality Grades form the foundation for the incremental changes in marbling scores that describe the marbling EPD. Everyone in the industry understands the increments used in the marbling EPD and how they are used in the real world. Likewise, the USDA Yield Grade (YG) formula for REA evaluation should become the standard for the reporting of the REA EPD. REA relative to carcass weight is how the YG formula works. (For example, to have average muscling, a 600 pound carcass needs 11.0 square inches of REA, a 700 pound carcass needs 12.2 square inches of REA, an 800 pound carcass needs 13.4 square inches of REA, etc. Yield Grade scores and carcass value are directly affected according to whether or not a carcass has more or less REA than what is average for a given carcass weight.) Unfortunately, the REA EPD is currently reported on an age constant basis without any relationship to carcass weight or the YG formula. REA at a constant age is meaningless in the real world because it allows growth to confuse the issue of muscularity. For example, high growth cattle can be light muscled but have strongly positive REA EPDs and heavy muscled cattle can be low growth and have negative REA EPDs. Can anyone explain how the current REA EPD can be used in a meaningful way?
Information from the American Angus Association (AAA) database supports a disturbing trend-that REA EPDs are increasing year over year while REA relative to carcass weight is decreasing. Remember, REA relative to carcass weight is how the YG formula works and how value is determined. Some back of the envelope calculations follow to support this claim.

For steers harvested between 360 to 480 days of age, the Fall 1999 AAA 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 steers in the database in 1999 were .52 square inches below the YG formula for average.

Similarly, for steers harvested between 360 to 480 days of age, the Fall 2009 AAA 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 have an average approximate 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 were .85 square inches below the YG formula for "average".

Interestingly, during the 10 year period between 1999 and 2009, the REA EPD increased by .2 square inches, while the kill data show that REA had actually decreased by .33 square inches on a carcass weight basis. The REA EPD is therefore very misleading as it is currently reported. Many breeders use the REA EPD hoping to increase red meat yield when in fact they may be selecting against red meat yield.

Just as the USDA Quality Grade formula establishes the increments used in describing the marbling EPD, the USDA Yield Grade formula should become the standard for reporting the REA EPD. In this scenario, a REA of "0" would mean a REA equal to the YG formula for average, a+.30 EPD would mean .30 square inches above average, a-.30 EPD would represent .30 square inches below average, etc.

Please consider the following example. There are two bulls, A & B, with progeny evaluated at the same age with the following carcass measurements: "A" has an average progeny REA of 13.1 square inches with an average carcass weight of 825 pounds while "B" has an average progeny REA of 13.1 square inches with an average carcass weight of 725 pounds. Under the current system, these bulls would have exactly the same REA EPD, but in reality have significant differences in muscularity. Using my suggested method of reporting REA EPDs, bull "A" would have a REA EPD of -.60 while bull "B" would have a REA EPD of +.60. (An 825 pound carcass needs 13.7 square inches of 4
REA to be average, so progeny of "A" are 13.1 - 13.7, or .6 square inches below average, while a 725 pound carcass needs 12.5 square inches of REA to be average, so progeny of bull "B" are 13.1 - 12.5, or .6 square inches above average.) This suggested method of REA reporting does a much better job of describing REA in the manner it is used in the real world.

The most beneficial REA EPD would be calculated as follows. First, change the endpoint from an age constant endpoint to a fat constant endpoint. A fat constant endpoint is a more accurate endpoint for real world evaluations than age or carcass weight and a fat constant endpoint reduces the effect of fat on carcass weight. Then use the YG formula as described above to report the REA EPD. This change can be accomplished immediately because it simply requires the data to be analyzed in a different manner and does not require the collection of any new information. In addition, the DNA markers for REA would need to be adjusted accordingly.

We have talked to a number of animal scientists and breeders about the issues raised herein. Every one agrees with our position that the REA EPD reporting needs to be changed as described and that information needs to be gathered on the effects of testosterone on marbling. Data gained from that research would then need to be analyzed and incorporated into the marbling EPD. Additionally, research would need to be conducted to determine if some DNA markers for marbling actually follow testosterone levels instead of marbling.

We respectfully request a reply at your earliest convenience to the concerns raised in this document.
Bobby Grove Don Benner Brooke Miller, M.D.
White Ridge Angus Benfield Angus Ginger Hill Angus
Somerville, VA Deerfield, VA Washington, VA
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