EPDs 101

EPDs 101

Expected Progeny Differences (EPDs) are a statistics that help us predict the performance ability of a sire or dam for certain traits relevant to beef production. Cattle breeders use EPDs to make comparisons between animals about their genetic potential. EPDs take into account an animal’s performance data (their own and any related cattle), pedigree, and if available, genomic testing information in their calculation.

If we were comparing two bulls to buy at a Shorthorn sale, these are the EPDs you might see listed in the catalog:

Calving Ease Direct (CED): The CED EPD is listed as a percentage of unassisted calvings. A higher CED EPD predicts a sire that will have a higher percentage of unassisted calves.

Birth Weight (BW): Compares the differences in the weight of calves at birth. It is measured in pounds, and cattle with higher BW EPDs are predicted to produce heavier calves.

Weaning Weight (WW): The WW EPD is expressed in pounds and predicts differences in weaning weight of a sire’s calves. Bulls with higher WW EPDs predict heavier calves across the scale at weaning.

Yearling Weight (YW): Just like WW, only at the next stage of life. The YW EPD is expressed in pounds. Higher YW EPDs are likely to produce bigger, heavier yearlings.

Milk (MK): The hardest trait to measure, since we don’t measure milk production in beef cows. The MK EPD is measured in pounds of calf weaning weight due to his mother’s milking ability. A higher MK EPD predicts that a bull will sire daughters who raise heavier calves due to their milk production.

Total Maternal (TM): Total Maternal EPD is a simple formula. TM= MK EPD + ½ WW EPD. It measures impact on calf weaning weight due to both milk production and the cow’s genetics for growth. Bulls with a higher TM EPD should sire daughters with a bigger impact on their calves’ weaning weight.

Calving Ease Maternal (CEM): Measures the ability of a bull’s daughters to calves unassisted as two year olds. The higher the CEM EPD, the easier calving should be when a bull’s daughters have that first calf.

Stayability (ST): Cows who work longer make more money. The ST EPD predicts the ability of a bull to sire cows that “stay around”. The ST EPD is shown as a percentage of how much more likely a bull’s daughters will stay in your herd to the age of 6. A higher ST EPD bull is more likely to have daughters stay around for a long time.

Carcass Weight (CW): The CW EPD is all about pounds of beef on the rail. Higher CW EPDs mean that a bull is more likely to sire feeders with heavier carcass weights.

Yield Grade (YG): The USDA Yield Grade scoring system is the unit of measurement for the YG EPD. Yield Grade 1 are leaner, more retail product carcasses. Lower, more negative YG EPD bulls are expected to sire calves that score better on the USDA Yield Grade scale.

Ribeye Area (REA): REA is measures the size of the muscle that gives us the ribeye in square inches. Higher REA EPDs indicate a bull is expected to produce larger ribeyes in their offspring.

Marbling (MB): The MB EPD is in units of percentage of intramuscular fat within the ribeye. Higher MB EPD bulls should sire higher marbling (and grading) feeder calves.

Fat Thickness (FT): Inches of backfat (in hundredths of an inch) is the unit of measurement for FT. More negative FT EPDs are indicative of a bull that should sire less backfat in his calves.

Selection indexes weight multiple EPDs with an economic value to create a simplified selection tool built to meet the goals of your operation. Whether it’s production of superior replacement females, quality feeder cattle, or sleep all night calving ease, selection indexes combine the traits that drive profits to identify the Shorthorn genetics suited to meet your needs.

$Calving Ease ($CEZ): Genetics that you can trust to calve easy while keeping mature cow size in check. You’ll sleep soundly and your heifers will thank you for selecting for high $CEZ sires.

$British Maternal ($BMI): A balanced, multi-trait index built to identify the ideal seedstock for crossbreeding on British breed cow herds. $BMI focuses on the traits you want in your cows: easy calving, maternal performance and moderate mature size, while keeping the growth and carcass merit in your steer calves.

$Feedlot ($F): For the cattleman who sees value in retaining ownership of feeder cattle. Growth, performance and carcass quality drive $Feedlot. Cattle bred to grow and grade excel in $Feedlot.


EPDs are able to give us an idea of what an animal can produce in our herd, but they aren’t perfect predictors. They need information feeding the calculations to make them better. We use EPD accuracies to help us determine the reliability of an EPD. Accuracy is expressed as a value from 0 to 1, with higher values giving us more confidence in that EPD value.

The EPDs on a yearling bull start with a baseline of the average between his parents, a very low accuracy EPD (less than 0.20). As his data is recorded, his EPDs change to reflect his performance and his accuracy will increase. Genomic testing will further increase accuracy (up to about 0.40), but large volumes of progeny performance data are what lead to high accuracy EPDs on a sire.

EPD Accuracies
Very Low Less than 0.20 Young cattle with little data
Low 0.21-0.40 Cattle with data and genomics
Medium 0.41-0.70 Young sires with progeny data
High Greater than 0.71 Heavily used sires

What is contemporary grouping?

Contemporary groups are truly the cornerstone of any genetic evaluation. Contemporary groups are defined as animals of the same breed composition, sex and similar age, which are raised under the same management conditions until the time of measurement. EPDs are calculated based on the differences reported among animals in the same contemporary groups. The following paragraphs outline a few cardinal rules to follow when establishing contemporary groups.

Rule #1: It Takes Two.

The basis of genetic evaluation is a comparison of animals given the same environmental opportunities. No matter how proud you may be of your top animal, his/her performance information has no value by itself and no impact on the EPDs of the elite animal; his/her sire or dam, relatives, etc. Individual animals need at least one other pen mate with which to compare. As the number of animals in a contemporary group goes up, the power of the information increases. In turn, EPDs will change at a faster rate and EPD accuracies will increase, moving cattle closer to their “true” genetic estimate.

Rule #2: Contemporary Groups Never Get Larger.

As cattle age, breeders make decisions that determine the fate of each calf in the herd. In many cases, the decision is performance based, keeping the faster growing genetics back in the herd. Contemporary groups are established at birth on the original farm or ranch where the calf was born. Purchased cattle obviously come from different operations, so they can never be contemporaries of your own home-raised progeny. Even if animals are fed in the same pen since weaning, their environmental opportunities (and their mother’s) were different prior to that, potentially affecting performance traits. In the complex matrix of performance records, herd of origin is the first limiting step in determining contemporary groups. As a result, any weaning and yearling data collected can dramatically influence the EPD profile of sires and dams.

Rule #3: The Bad Ones Make the Good Ones Better.

This statement seems like an oxymoron of sorts, but the disadvantages of selective reporting cannot be made clearer. Many breeds are migrating to a performance system that mirrors the ASA Whole Herd Reporting (WHR) system. This system encourages breeders to submit ALL records for their calf crop, creating a data set that is a much truer reflection of the herd’s genetic value. Reporting only calves that remain in the herd skews data and actually hurts the resulting EPDs of the most elite progeny.

Can I compare EPDs of different breeds?

Until recently EPDs of different breeds of cattle could not be compared directly because each breed had different baselines and points of reference. This has changed in recent years as breed associations have switched to the multi-breed genetic evaluation conducted by International Genetic Solutions (IGS). IGS is the largest multi-breed genetic evaluation in the world with a database of over 19,000,000 animals with 400,000+ animals added annually

to its database. IGS is a collaboration of 12 different breed associations across the U.S. and Canada. The American Shorthorn Association has been a part of this progressive group of associations since 2014. Shorthorn EPDs can be compared directly to the following breeds of cattle: Canadian Angus, Canadian Shorthorn, Chianina, Gelbvieh, Limousin, Maine-Anjou, Red Angus and Simmental.

If you have additional questions about the ASA or EPDs, please contact: 

The ASA office 816.599.7777