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Understanding EPDs

published: October 16th 2009
by: Evan Whitley, Noble Foundation
source: American Simbrah Breeders

Expected progeny differences (EPDs) are one of the most useful tools cow-calf producers have at their disposal. Their usefulness is paramount due to the importance of selecting and purchasing the right bull for commercial (and purebred) operations. Yes, you read right — I am proposing that even commercial operations use EPDs in sire selection. In the past, the perception was that EPDs were only for the purebred folks or the bigger producers. Not so anymore, primarily due to the fact that the beef industry has evolved into one that covets information now more than at any time in its history.

One of the results of this change is more and more bulls are sold with EPD information than at any time in the past. This is a good thing, because it provides one more tool to be placed in the tool belt of a potential buyer to ensure they purchase the right bull and will be happy with the results. However, it is my contention that because EPDs are so prevalent in our industry, we reference them in conversation without really knowing what they are and, more importantly, how to use them.

What Are EPDs?

Simply put, EPDs are an estimate of how a particular bull's calf will perform in certain traits compared to another bull's, in that particular breed and when bred to similar females, before the mating ever occurs. The actual EPD is calculated using information submitted to the breed associations and provides a basic representation of the pedigree for that particular bull for a particular trait of interest. It is very important to realize that EPDs are not static, they will change over time as more and more progeny information is collected, which leads us to another term of interest: accuracy. Accuracy is just that, how accurate or reliable an EPD is. It is measured on a scale from 0 to 1, the higher the number, the greater the accuracy. Accuracies are important when assessing existing bull batteries that may have animals of varying ages and when looking at pedigree information. However, when actually making purchasing decisions, most of the pool of animals you will be selecting from will be relatively young, having produced no progeny, and therefore will have relatively low accuracies for their individual EPDs. This is where going back and looking at pedigree EPDs and accuracies for potential purchases becomes useful.

How Do You Use Them?

First of all, the process involves outlining your goals and objectives for this particular purchase. This enables you to hone in on those traits that are most important to your operation, and therefore will allow you to select a bull that meets those objectives. For example, let's assume you are a producer who places priority on weaning weight. You have two bulls to choose from within your chosen breed that will complement your cow herd. Figure 1 shows that the weaning weight (WW) EPDs for Bull A and Bull B are 31 pounds and 46 pounds, respectively, and their accuracies are about the same. What does this mean? It means that on average, Bull B will sire a calf that will wean, at the same age, 15 pounds (46-31=15) heavier than calves sired by Bull A, when bred to a similar set of cows. OK, but is that good or bad?

In order to answer that question, you need another very important piece of information, which is the percentile breakdown charts found in the sire summary for your breed of choice. This chart allows you to look at the breed as a whole and determine where an individual's EPD fits within the breed. As you can detect from Figure 1, Bull B is in the top 10 percent for weaning weight within the breed. The choice is pretty clear, isn't it, of which sire to attempt to purchase? Perhaps not, because we have only looked at one trait for the bull in question. Remember, single trait selection has gotten us into trouble in the past, and we don't want to revisit history. To avoid extremes in any one trait, be aware of, and comfortable with, all of a bull's EPDs that are important to you before making the purchase. EPDs are a tool that can make us better managers if we know how to use them, what their limitations are and if they are used in conjunction with other pertinent information. If you are interested in learning more about EPDs, I suggest picking up a sire summary for your breed of choice and familiarizing yourself with it prior to purchasing your next bull.

Quick Guide to ASA EPDs For Simbrah and $ Indexes

For more detailed information about EPDs and $ indexes, visit www.simmental.org. List-ed below are the units in which ASA EPDs are expressed for Simbrah cattle:

All-Purpose Index (API): Dollars per cow exposed under an all-purpose-sire scenario. (See $ Indexes for more details)

Back Fat (BF): Inches of carcass backfat at 475 days.

Birth Weight (BW): pounds of birth weight

Carcass Weight (CW): Pounds of carcass weight at 475 days.

Milk (MILK): Pounds of weaning weight due to milk.

Marbling (MRB): Carcass marbling score at 475 days.

Maternal Weight Weight (MWW): Pounds of weaning weight due to milk and growth.

Ribeye Area (REA): Square inches of carcass ribeye at 475 days.

Stayability (STAY): Per-cent of daughters remaining in the cowherd at six years of age.

Terminal index (TI): Dollars per cow exposed under a terminal-sire scenario. (See TI for more details)

Warner-Bratzler Shear Force (WBSF): Pounds of force required to shear a ribeye steak

Weaning Weight (WW): Pounds of weaning weight

Yearling Weight (YW): Pounds of yearling weight

Yield Grade (YW): Carcass yield grade score at 475 days.

$ Indexes: Though EPDS allow for the comparison of genetic levels for many economically important traits, they only provide pieces of the economic puzzle. This is where $ indexes come in. Through well-conceived, rigorous mathematical computation.

$ indexes blend EPDs and economics to estimate an animal’s overall impact on integrated commercial production. The same technology that led to the dramatic progress in swine, poultry and dairy genetics over the last several decades was used to develop the following $ indexes:

All-Purpose Index (API): Evaluates sires for use on the entire cowherd (bred to both Angus first-calf heifers and mature cows) with the portion of their daughters required to maintain herd size retained and the remaining heifers and steers put on feed and sold grade and yield.

Terminal Index (TI): Evaluates sires for use on mature Angus cows with all offspring put on feed and sold grade and yield.

Using API and TI: First, determine which index to use; if you are keeping replacements use API, if not, use TI. Then, just as with EPDs, zero in on the unit difference between bulls. (As described above, index units are in dollars per cow exposed.) The difference can be used to determine how much a bull is worth compared to another. Put another way, how much you can pay for one bull compared to another. For example, when buying on all-purpose-type sire, you can quickly figure a bull score +100 for API is worth an extra $6,000 over a +50 bull if both are exposed to 30 cows over 4 years ($50 diff. x 30 hd) x 4 yr=$6,000). A percentile ranking chart is required to determine where a bull’s index value ranks him relative to other bulls in the breed. For more detailed information about EPDs and $ indexes, visit.www.simmental.org.

Important disclaimer: DO NOT compare index values of purebreds of different breeds, hybrids of different breed composition or purebreds with hybrids—our system was not developed to make valid comparison among these groups. Therefore, you must first determine the breed and breed composition, appropriate for your herd and use index values to compare animals within that population.