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Breeding, Genetics & ReproductionExpected Progeny Differences Explained
An expected progeny difference, or EPD, is a prediction of how a parent's calves are likely to perform compared with calves from other parents. Read it correctly and it is one of the most useful tools in beef breeding.
Key points
- An EPD predicts the difference a parent passes on, relative to others in the same breed.
- Compare EPDs only within a breed.
- Accuracy shows how stable the number is likely to be.
- Use target ranges across several traits instead of one top number.
- EPDs support, but do not replace, soundness and structure checks.
What an EPD actually says
An EPD predicts the genetic difference a sire or dam will pass to the next generation for a given trait. It is expressed in the units of that trait, such as pounds for weights. It is a comparison, not a guarantee.
If one bull has a higher weaning weight EPD than another, his calves are expected, on average, to wean heavier when both are bred to similar cows under similar conditions. Individual calves vary, but across many calves the difference shows.
Compare within a breed, not across breeds
EPDs are calculated within a breed association's database, so they are only directly comparable between animals of that same breed. A number from one breed cannot be set next to a number from another breed.
If you are comparing bulls of different breeds, ask the associations whether they publish across-breed adjustment information, and ask your extension specialist how to use it.
Understanding accuracy
Every EPD comes with an accuracy value that reflects how much information sits behind it. A young bull with few progeny records has a lower accuracy, which means his EPD could move up or down as more data arrives. An older sire with many recorded calves has a higher accuracy and a more stable number.
Low accuracy is not bad. Young sires are how breeds improve. It simply means you should expect some movement, and you may want to spread risk across more than one young bull.
Common EPD groups
Breed associations publish EPDs in several families. The names differ a little between breeds, so read the association's glossary for exact definitions.
Most families fall into the groups below. Ask your breed association or extension specialist which ones matter most for your operation.
- Calving ease: how easily the sire's calves are born
- Birth weight: a predictor of calf size at birth
- Weaning weight: growth to about 205 days
- Yearling weight: growth to about 365 days
- Maternal milk: the milk contribution of his daughters
- Carcass traits: predicted merit of finished progeny
- Fertility and stayability traits where published
Reading a sale catalog with EPDs
Catalogs usually print EPDs alongside percentile ranks within the breed. A percentile tells you where the bull sits compared with the rest of the breed, which helps put a raw number in context. Ask the association how the percentile table is built and how recent it is.
Circle the traits that matter for your herd first and read those before anything else. If the numbers on those traits fall inside your targets, then look at the bull in person. Never buy from the numbers alone: feet, legs, eyes, scrotal development and temperament are not in the catalog.
Many associations now blend genomic test results into EPDs, which can raise the accuracy for young animals before they have progeny of their own. This does not change how you read the number, but it can make a young bull a less risky choice than it once was.
How to use them when buying
Set target ranges for the traits that matter to you before looking at bulls. Eliminate bulls that fall outside your needs, particularly on calving ease if you breed heifers. Then use visual appraisal, structure and a breeding soundness exam to choose among those that remain.
Avoid making a purchase on a single EPD. A bull with the top number on one trait can be well below average on another.
Mistakes to avoid
The biggest error is treating an EPD as the actual weight a calf will have. Another is comparing bulls from different breeds directly, or ignoring accuracy.
Also remember that EPDs get updated. A number printed in a sale catalog may be a little different by the time the bull is in your pasture.
- Do not read an EPD as a promise for any single calf
- Do not mix breeds in a direct comparison
- Check accuracy before relying on a young sire
- Update your numbers from the association site
Sources and further reading
- Beef Improvement Federation
- American Angus Association
- American Hereford Association
- University of Nebraska-Lincoln Beef
Organization homepages are linked so you can search them for current guidance on this topic.