EPDs 101

EPDs 101

EPDs can be difficult, overwhelming, and downright confusing!  However, they are also useful to help you breed better Shorthorn cattle. The purpose of EPDs is to calculate how we expect the offspring of an animal to perform for specific traits.

Calving Ease Direct (CED): Calving ease direct measures the ease of which a bull’s calves are born when he is bred to first calf heifers. The calving ease scores you turn in go into the calculation of CED. Birth weight EPD also plays a role in CED (about 70%), as the two traits are correlated. CED is reported as a percentage of unassisted births. A higher CED EPD is associated with a higher percentage of unassisted births. With BW being a portion of CED, selecting for both traits is, in reality, double selecting for birth weight. It is recommended to choose one or the other to emphasize, with many people choosing CED, as having a live unassisted calf is an economically relevant trait to cattle producers.

Birth Weight (BW): Birth weight simply measures the differences in weight of calves at birth, and is reported in pounds. The birth weights that you report on calves go into the calculation of the BW EPD. A lower BW EPD indicates a lower birth weight. Birth weights (and all other traits) are compared in contemporary groups that compare males to males and females to females, born within a 90 day window. The contemporary groups that start at birth are the building blocks for future data collection. These groups can only get smaller after birth, as cattle are removed from those groups.

Weaning Weight (WW): Weaning weight measures the differences in weight of calves at weaning, and is also reported in pounds. Weaning weight data reported to ASA is adjusted to a 205-day WW and used in the calculation of the WW EPD. A higher WW EPD indicates a higher weaning weight.

Yearling Weight (YW): Like other weight traits, YW measure the differences in weight of animals at a year of age, and is also expressed in pounds. Higher YW EPDs indicate a higher expected yearling weight. Yearling data turned in is adjusted to a 365-day YW and used for EPD calculation. WW and YW are correlated traits, so if there’s change in WW, you can also expect a change in YW in the same direction.

Milk (MK): Milk EPD is, by definition, the expected differences in a bull’s daughters’ calves at weaning weight due to their milking ability. The Milk EPD measures how well daughters milk and how that translates to the weaning weights of their calves. Weaning weight data from the offspring of a bull or cow’s daughters drive the MK EPD calculation, even moreso than the data of an animal’s own progeny. A higher MK EPD indicates a higher weaning weight due to the bull’s daughters’ milking ability.

Total Maternal (TM): TM predicts the TOTAL difference in weight of a bull’s daughters’ calves at weaning. A portion of this difference in weight comes from the milking ability of the bull’s daughters (MK EPD), and a portion comes from the genes for growth passed from the bull to his daughters and then on to their calves. The TM EPD is calculated by taking ½ of a bull’s WW EPD + his MK EPD.

Calving Ease Maternal (CEM): CEM indicates the ability of a bull’s daughters’ give birth unassisted as first-calvers, and is expressed as a percentage.  A higher CEM indicates a higher percentage of unassisted births.

Stayability (ST): Stayability is a measure of the percentage of a bull’s daughters that will still be in the herd at six years old. Stayability is expressed as a percentage. A higher ST EPD indicates a higher percentage of daughters staying in the herd. The disposal codes on your WHR Herd Inventory are used in stayability calculations. It’s important to use proper disposal codes for cattle that leave your herd.

Carcass Weight (CW): Carcass weight is like other weight traits. It’s expressed in pounds and measures the differences in carcass weight of a bull’s progeny. Higher CW EPDs indicate heavier carcass weights.

Ribeye Area (REA): REA measures the difference in ribeye area of a bull’s progeny. REA is measured in square inches. A higher REA EPD is indicative of larger ribeyes. Carcass and ultrasound data reports sent to ASA are a part of the evaluation of REA. Typically, higher growth cattle are also higher REA cattle, as the traits are correlated.

Marbling (MB): The MB EPD measure the amount of intramuscular fat (marbling) within the ribeye.  It is measured as a percentage of intramuscular fat. A higher MB EPD is associated with higher marbling. Carcass records and ultrasound are used in the calculation of the MB EPD. Marbling and ribeye area are traits that are inversely correlated, meaning that as one goes up, the other tends to decrease. That is why it is more difficult to find cattle who ratio high for both traits and have high EPDs for both traits.

Fat Thickness (FT): Fat thickness measures the amount of back fat on a carcass. FT is reported in inches. A lower FT EPD indicates a bull whose progeny will have less fat on the carcass than a bull with a higher FT EPD.


The three selection indexes published by ASA provide a tool for optimally weighting an EPD which has economic importance to various defined breeding objectives, such as breeding heifers or a maternal or terminal scenario. These indexes attempt to eliminate single trait selection, as several of the EPDs discussed above are combined into the calculation of the index.

Calving Ease Index ($CEZ): This index assumes a bull will only be mated to heifers. The potential profitability of the sire is measured by the incidence of live calves at birth. Naturally, $CEZ places an emphasis on CED.  Moderate mature size is also emphasized in the index, but performance is not a priority.

British Maternal Index ($BMI): This multi-trait selection index attempts to measure a bull’s potential profitability when complimenting the British cow base (Angus, Red Angus, Hereford, etc.) in a maternal breeding program.  Shorthorn females can likewise be gauged at adding value to British or British-composite bulls of other breeds.  A balance of growth (WW) and carcass traits(REA, Fat, MB) is desired with a strong maternal component (CED, Milk, CEM) aimed at moderate mature size (YW), optimum reproductive efficiency and cow longevity.

Feedlot Index ($F):  $Feedlot places heavy emphasis on growth (WW, YW) and carcass traits (REA, Fat, MB) but also looks to minimize calving difficulty (CED).  This multi-trait index assumes the sire will be mated to a mix of heifers and cows and attempts to measure profitability when progeny are sold on the fed market.  On the female side, mature size should be monitored closely when selecting for $F.



What is accuracy?

The accuracy of an EPD is a measure of the confidence of the genetic merit prediction. Accuracy of an EPD ranges from 0 to 0.99. As EPD accuracy increases, you can be more confident that the EPD is a true indicator of an animal’s genetic merit. Accuracies increase as more performance data is recorded on progeny and relatives of an animal. When looking at the accuracy of an animal’s EPDs, here are some rules of thumb to consider:

Accuracy less than 0.40: Low accuracy. Young animals and animals with little recorded progeny performance data will generally have low accuracy EPDs. Low accuracy EPDs are the most apt to change.

Accuracy 0.41-0.60: Medium accuracy. Animals have some progeny data recorded, but there is still possibility for medium accuracy EPDs change.

Accuracy 0.61-0.80: High accuracy. Animals have large quantities of progeny data recorded. EPDs in this range can be used with confidence.

Accuracy greater than 0.81: Very high accuracy. The animals with the greatest amounts of progeny data fall into this category. EPDs are unlikely to change and can be used with strong confidence.

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