Expected progeny differences (EPDs) are an important tool producers utilize when selecting genetics for their herd. In addition to EPDs, the American Gelbvieh Association (AGA) publishes tools to help producers better utilize these EPDs such as accuracy, possible change, and percentile rank. Below we explain what these values mean and where they can be found on animal's within the AGA Herdbook.

An EPD is an estimate of animal's genetic merit for a given trait. More simply, an EPD estimates the genetic value of an animal as a parent for the next generation.

There are three types of information utilized to calculate an animal’s EPD:

In other words, all data that is collected and relates to the animal of interest is utilized to calculate its EPD. 

An accuracy value is a measure of the reliability associated with the EPD. Specifically, accuracy measures the strength of the relationship between the genetic prediction (EPD) and true genetic value. As an animal transitions from a non-parent to a parent, more information is reported and used in the weekly genetic evaluation. Ultimately, a breeder can use accuracy to monitor the value (amount and quality) of the information used for EPD calculation.

Accuracy is reported with a range of zero to one. As accuracy approaches 1.0, the EPD is more accurately estimating the true genetic merit of an animal for a given trait. Although low-accuracy EPDs are less reliable than the high-accuracy EPDs achieved by proven sires, EPDs remain the most powerful tool to describe an animal’s true genetic merit and are significantly more effective in causing genetic change than the use of actual measurements or ratios.

Accuracy values are published with every EPD and can be found on the AGA registry listed as "acc" on the EPD chart. 

An EPD will change due to the information that is being submitted on the sources utilized to calculate an animal’s EPD. As described above, if more performance data is submitted by a producer on animals that are related to your bull (i.e. progeny, sisters, half-brothers, genotypes) then his/her EPD is likely to change based on the data being collected. 

As information is added, an animal’s EPDs are expected to change closer to the animal’s true genetic value. Thus, the expected amount an EPD could possibly change at a given level of accuracy is known as the ‘possible change value’ (PCV). 

PCVs are expressed in the units of the specific trait and are used to illustrate the range in which an animal’s true genetic value is likely to fall. A possible change value is the amount an EPD may be expected change at a given accuracy, where an animal’s true genetic value for each trait expected to fall within one PCV two-thirds of the time.

This value is found on the registry and is listed as +/- on the EPD chart. For more information on possible change value, click below to read a full Gelbvieh World article.

Percentile rank is a useful tool when looking at EPDs and how that animal ranks amongst others in the population. The AGA publishes percentile rank on animals that are in similar stages in production (active sire, active dam, and non-parent) and separated by breed percentage (Gelbvieh, Balancer, or all). The category in which your animal is being ranked with can be found with the animal’s EPDs on their detail screen.

Percentile rank is a great item to publish on animals in a sale catalog and can help customers more easily interpret the EPDs.

Along with the EPD value, the AGA publishes the above mentioned possible change, accuracy, and percentile rank for EPDs on animals in the herdbook. This can be found on the animal detail screen under the EPD tab.

Below is an example of what can be found on the animal’s EPD tab:

For more information or questions about EPDs, please contact the AGA office at 303-465-2333 or email [email protected].