FEATURE ARTICLE
EXPECTED PROGENY DIFFERENCES: THE BEDROCK OF GENETIC IMPROVEMENT Editor’s Note: A comprehensive version of this article including index mathematical calculations can be found online at GoBrangus.com.
by Darrell Wilkes, Ph.D., IBBA executive vice president After 40-years of speeches and writing about EPDs, it is apparent from the calls we receive from breeders that some of the most fundamental truths about EPDs are still not well understood. Every survey that’s been done in the past decade has confirmed that commercial cattlemen utilize EPDs in their bull selection process. Bull customers expect you, as a seedstock producer, to understand EPDs and to be able to answer their questions on this subject. Therefore, perhaps one more article on EPDs will sharpen your explanations to your customers. At the end of this article, I will actually show how to compute an EPD from scratch. Don’t worry, it’s easy. You can do the math in your head. When EPDs were introduced to the beef industry in the late 70s, the scientists said that EPDs were seven to nine times more powerful than individual weights and measures with regard to making genetic change. Since then, the equations have been improved, and computers are much more powerful, which makes complex equations easier to handle. We have also added the value of genomic testing to EPDs. If EPDs were seven to nine times more powerful than individual weights and measures back then, I would argue that they are at least 10-times more powerful than individual data today, probably 12-15 times more powerful. Although obvious, it helps to restate the fact that EPDs can be used to compare animals across an entire breed or other population of cattle whose data are kept in the same database. Individual weights and measures ONLY have relevance within a single herd, and within a legitimate contemporary group. There simply is no dispute: If you want to make purposeful and I used to ask my students: Would you be significant genetic better off to buy a bull with a 110 YW ratio change in a out of a herd with an average yearling population of weight of 1,200, or would you be better cattle, EPDs are off to buy a bull with a ratio of 100 out of the single most a herd with an average yearling weight powerful piece of 1,320? Both bulls weigh 1,320. Which of information one has a higher breeding value for available to you. yearling growth? I’d let them argue about Astute breeders this for several hours before they finally know this and concluded [correctly] that the best way to are trying to select the bull with the highest breeding move away value for yearling growth is just to flip a from publishing coin. EPDs can fix that. individual
weights and measures in their sale catalogs and advertising. It is a delicate balancing act because many commercial customers still want to see the actual data; such as birth weight, weaning weight, etc. Individual weights and measures are still printed in advertisements even by people who understand EPDs and know darn well that they should not be confusing things by publishing raw data – such as actual rib eye area or an amazing %IMF value. In a perfect world, we would never publish individual weights and measures again. But, the world isn’t perfect. Realizing that success in the seedstock business requires genetics AND marketing, I cannot begrudge anybody for bragging about an amazing individual record. As time goes on, however, I hope we see less of that. The first and most fundamental TRUTH about EPDs is that they absolutely do NOT predict an actual weight or measure. A common call into the office goes something like this, “If I buy a bull with a +25 for Weaning Weight (WW), what will my calves weigh at weaning?” An EPD will not give you an answer to that question. Here’s how I answer that question: “I have a neighbor who is a great stockman. He rotates pastures like a pro and has virtually no weeds. No matter the weather, grass always seems to be growing on his place. His water tanks are clean. He buys top end mineral and his mineral feeders never run out. His cattle are never sick. He even has a low fly population. I hate that guy (though I’d like to be like him). He buys Brangus bulls with +25 EPD for Weaning Weight. He weans a 97% calf crop and they weigh 600 lb. I’m not that good. My pastures are mostly weeds and brush (from poor management). My water source is mostly mud puddles. I figure plain old salt is the only mineral they need. I doctor or bury 15 percent of my calves and the darn cows are always thin. But I buy “better” bulls, with WW EPD of +35 and then I wean calves weighing 475 lb. Those darn EPDs don’t work.” EPDs absolutely “work.” If the good manager, as described, bought some bulls with +35 EPD for WW and ran them in common with his +25 WW bulls, we would expect to see a 10 lb. difference in weaning weight between the two sets of calves. However, if the poor manager upgraded his bull purchases to bulls with +50 WW EPD, he may see no difference at all in the average weaning weight of the calves sired by his +35 bulls simply because his environment is so limiting that genetic differences have no opportunity to be expressed. (continued on page 22)
21
