Frequently Asked Questions about Expected Progeny Differences
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 are EPDS?
Expected progeny differences (EPDs) are a very important tool used in genetic selection. EPDs are used to compare the differences in predicted performance of animals’ offspring for specific traits. Calculation of EPDs is driven by pedigree, progeny, and individual performance data. The American Shorthorn Association offers twelve different EPDs for specific traits. Additionally, ASA provides three economic ($ Value) indexes, providing a single value for the selection of breeding stock that optimizes selection on a number of traits that define profit in a particular production scenario.
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): Reflects a bull’s ability to sire daughters who calve unassisted. The value is expressed as a percentage of unassisted births, with a more positive number being 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): Weaning weight measures the differences in weight of calves at weaning, and is also reported in pounds. A higher WW EPD indicates an expected higher weaning weight.
Yearling Weight (YW): Like other weight traits, YW measure the differences in weight of animals at yearling, and is also expressed in pounds. Higher YW EPDs indicate a higher expected yearling weight.
Milk (MK): the expected differences in a bull’s daughters’ calves at weaning weight due to their milking ability. Milk is looking at how well daughters milk and how that translates to the weaning weights of their calves. 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.
Stayability (ST): The newest addition to the Shorthorn EPD lineup, Stayability is a measure of the percentage of a bull’s daughters that will still be in the herd at six years old. Like CED and CEM, Stayability is expressed as a percentage. A higher ST EPD indicates a higher percentage of daughters staying in the herd.
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): 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.
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 expected larger ribeyes.
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 Britishcomposite 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 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