Expected Progeny Differences—EPDs
The beef cattle industry continues to use EPDs as a selection tool in improving calf productivity. An EPD is the difference in performance (measured in pounds, percent, inches, etc.) expected in progeny, or offspring, of individual sires.
Sire summaries are produced and published by breed associations to provide up to date genetic evaluations on progeny of proven sires within their breeds. The sire summary formats may vary between breeds. However, they are designed to use unbiased prediction procedures to EPDs for all cattle in their breed that have legitimate performance records or progeny with legitimate performance records.
An EPD is always the best estimate of an animal’s genetic worth given the data for analysis. EPDs provide a genetic description of an animal for the traits included in the analysis. They are expressions of the relative genetic merit of beef cattle for various traits.
While EPDs are used to compare the predicted progeny performance between two animals (bulls or females) within a breed, regardless of herd location or age, they cannot be used to compare two animals of different breeds.
Since EPDs are used to compare two bulls (or females) within a breed, the difference in the EPDs for those animals compared would be the predicted differences in the average performance of those two animals’ progeny. For example, consider the EPDs for the bulls in Table 1.
Table 1. Birth Weight, Weaning Weight, and Yearling Weight EPDs for two bulls.
| EPD, lb. | |||
|---|---|---|---|
| Bull | BW | WW | YW |
| A | +5 | +22 | +40 |
| B | −1 | +7 | +30 |
| Difference | 6 | 15 | 10 |
These EPDs do not mean that bull A would increase birth weights by 5 lbs. and add 22 lbs. to the calves at weaning and 40 lbs. to the calves as yearlings. They simply allow us to predict the difference between the average weights of the two bull’s calves if they were mated to the same group of cows. When compared to bull B, we can expect calves from bull A to average 6 lbs. more at birth, 15 lbs. heavier at weaning and 10 lbs. heavier as yearlings.
In addition to the numerical EPD (can be + or −), an accuracy value (ACC–0.00 to 1.00) for that EPD will also be calculated during the breeds genetic evaluation analysis. This is a measure of confidence that the EPD reflects the true genetic merit of an animal.
Across–Breed EPDS
For years, animal scientists have told cattle producers that expected progeny differences (EPDs) should not be compared across breeds because they were developed as a measure of genetic merit for comparison within breeds. But over the past decade, across–breed EPDs (AB–EPDs) have been developed to help manage genetic uniformity when multiple breeds are rotated in a crossbreeding system.
By using the across–breed adjustment factors, animals of different breeds can be compared on the same EPD scale. This helps avoid large fluctuations in traits such as birth weight and milk. Initial research work on across–breed EPDs was a major part of the program at the Beef Improvement Federation. Understanding how to use both within — and across–breed EPDs is important for the successful production of beef cattle with the genetic potential to excel in their environment.
- http://www.ext.vt.edu/news/periodicals/livestock/aps-05_08/aps-447.html
- http://www.beefimprovement.org/2007_ABEPD_press_release.pdf
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