Frequently Asked Questions about Expected Progeny Differences

What are EPDs?

EPD stands for Expected Progeny Differences and are exactly what the name implies, the expected differences in the performance of progeny when compared to other animals of the same breed whose EPDs where calculated in the same analysis.  EPDs are calculated using different performance data from the individuals’ pedigree, progeny and individual performance.  The actual number value of the EPD has no real significance as EPDs are meant to be used on a comparative basis.  For example, a sire with a +2.0 birth weight EPD will be expected to produce calves that are 2.0 pounds heavier on average than a sire with a 0.0 birth weight EPD.  The American Shorthorn Association offers eleven different EPDs on animals recorded in their herd book in addition to calculating three $Value indexes.  These EPDs are recalculated and updated twice a year (spring and fall).  Below is a brief explanation of each EPD and $Value.


Calving Ease Direct (CED) – The most important EPD in sire selection for use on heifers.  This value is expressed as a percent of unassisted births; the more positive a number is the more desirable.


Calving Ease Maternal (CEM) – If planning to retain daughters from a particular bull then CEM is very important.  The value is expressed as a percent of unassisted births; CEM reflects a bull’s ability to sire daughters who calve unassisted.  The more positive a number is the more desirable.


Birth Weight (BW) – an indicator of birth weight and calving ease.  Larger BW EPDs typically, but not always indicate more calving difficulty.


Weaning Weight (WW) – an indicator of growth from birth to weaning measured from adjusted 205 day weights.


Yearling Weight (YW) – an indicator of growth from birth to one year of age measured from adjusted 365 day weights.


Milk (MK) – measured in pounds of calf attributed to milk at weaning.


Total Maternal (TM) – a combination of weaning and milk EPDs this number expresses a cow’s ability to bring in a heavier calf at weaning.


Carcass Weight (CW) – expressed in pounds as a predictor of the differences in hot carcass weight of a sire’s progeny compared to progeny of other sires.


Marbling Score (MB) – evaluation of intramuscular fat deposition in the ribeye as expressed in USDA numeric marbling scores.  Higher values indicate genetics that are expected to marble and have a higher quality grade.


Backfat (FT) – measured between the 12th and 13th ribs and expressed in inches.


Ribeye Area (REA) – expressed in units of square inches and offers genetic differences in muscularity at the 12th rib.

Calving Ease Direct ($CEZ) – This index assumes a bull will only be mated to heifers, not cows. The potential profitability of the sire is measured by the incidence of live calves at birth.  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.).  Shorthorn females can likewise be gauged at adding value to British or British-composite bulls of other breeds.  A balance of growth and carcass traits is desired with a strong maternal component aimed at optimum reproductive efficiency and cow longevity.


Feedlot ($F) – $Feedlot places strong emphasis on growth and carcass traits.  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 and how do I use it?

Accuracy is the strength of a particular EPD or the confidence one can place on an EPD.  Accuracies range from 0-.99 and are an indication how much an EPD can change.  As the accuracy approaches 1 the probability of the EPD dramatically changing decreases.  Higher accuracy individuals have more performance data reported from progeny and relatives.  For example, if you were selecting between two bulls to use on heifers that both have a birth weight EPD of +.1, but one sire has a high accuracy of .90 and the other has a low accuracy of .30; we would have more confidence that the sire with the .90 accuracy would be more apt to sire low birth weight calves.


Accuracy rules of thumb

Low (less than .40) – unreliable, but still best guess

Low/Medium (.40 – .60) – still some possible change.

Medium/High (.60 – .80) – reliable use with fair confidence.

High (greater than .80) – little degree for change, use with confidence.


What is a contemporary group?       

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 drop, 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.  The example below shows the pit falls of selective reporting weaning weight in a group of calves.

Calf ADJ. 205 WW Only The Top Calves Reported Ratio All Calves Reported Ratio
1 475 83
2 490 85
3 500 87
4 525 91
5 530 92
6 575 89 100
7 625 97 109
8 650 101 113
9 675 105 117
10 700 109 122
Avg. Wt. 645 575


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 16,000,000 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