Always Changing

by Lindsay Upperman, Ph.D., Director of Breed Improvement

There’s a saying by John C. Maxwell that states, “Change is inevitable. Growth is optional.”

However, when the changes aren’t necessarily expected or wanted, the ability to grow can be challenging, at best. There is no exception when genetics come into the picture. Especially around bull sale season, the questions start picking up about EPDs changing and why it occurs.

In last month’s Red Angus Magazine breed improvement article, there was discussion of how genes are passed from parents to offspring and how additional information is then incorporated into the EPDs. Remember, an EPD is an estimate based on information such as an animal’s actual performance, progeny or other relative’s performance, and genomic data.

After genomic data is submitted on the animal, the EPDs are then referred to as GE-EPDs or genomically enhanced EPDs. Essentially, if EPDs are changing, this means that data has been recently submitted from one of the sources discussed above and utilized to calculate the updated EPDs. As data is submitted, the EPDs may increase, decrease or stay the same – this all depends on the data. Additionally, the data will also result in an increase in the EPD accuracy.

Accuracy is a measure of the reliability of the calculated EPD and reflects the amount of information that is utilized in the calculation. Another way of looking at accuracy is the relationship between the calculated EPD and the true genetic merit of the given animal.

Accuracy values range from 0 to 1.0, with a larger value (closer to 1.0) meaning more information has been submitted. Along with accuracy, a measure of the average amount that an EPD could change over time is called Possible Change, which is depicted in Table 1.

From Table 1, with an accuracy of 0.6, the possible change is + 6.5 units for WW EPD. So, for example, with a WW EPD of 64 about two-thirds of individuals are expected to have a true progeny difference between 57.5 and 70.5 (64 + 6.5). Notice that as the accuracy increases, the possible change range decreases. Thus, at 0.9 accuracy, there is only a + 1.6, which is very little change. However, an accuracy this high is only possible for animals with hundreds of progeny records.

An accuracy value tends to go hand in hand with the amount of confidence a producer will associate with their animals’ EPDs. For example, a producer may associate a lack of confidence with a younger animal’s EPDs, as they tend to have fewer progeny records or even less performance data collected – think of traits such as yearling weight, carcass records or even heifer pregnancy.

The opposite may be true for an older animal as it has had the chance to have multiple progeny records be collected, especially an older bull or AI sire with his daughters’ records being collected for traits such as Stayability. However, time is of the essence, so how does a producer have more confidence in a younger bull?

In regard to all the available sources of information, genomic testing is the quickest way to increase accuracy and get closer to an animal’s true genetic value as a parent, especially when considering the amount of time involved. For instance, it takes four to six weeks to run a DNA test compared to collecting data on progeny which can take at least two years, depending on the trait.

One way to consider the information or knowledge gained from genomics is to find the equivalent number of progeny records that an animal would need to see a similar increase in accuracy.

In Table 2, a genomic test is equivalent to adding more than 25 calves for calving ease, 15 records for Stayability or even 10 carcass records for Marbling.

Ultimately, change is always occurring in regards to EPDs. These changes are due to information being submitted through the various sources described in Table 2.

Furthermore, accuracy and possible change are values to help account for the amount of information and the reliability of the EPD, as well as a measure of the average change one would expect an EPD might change.

So, if change is inevitable, let’s hope that your animals’ EPDs grow (in the right direction)! //

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