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Angus Association releases single-step, seeing better accuracy in EPDs

Jaclyn Krymowski for Progressive Cattleman Published on 24 October 2017

July 7, 2017, marked a big day in Angus history, as the American Angus Association released its single-step method – an evaluation for the breed genomically enhanced expected progeny differences (GE-EPDs).

The association, through Angus Genetics Inc. (AGI) working with the University of Georgia, released single-step to generate EPDs more accurate and effective than those procured from the former multi-step method. In the multi-step, genomic information from genotyped animals were used to predict molecular breeding values; the molecular breeding values were then used as correlated traits in the association’s genetic evaluation for each animal.

Single-step can incorporate performance and pedigree information, genomic testing and progeny data into a single GE-EPD all at once; a new direct genomic value replaces the former molecular breeding value. The result not only allows the use of more data and increased accuracy to benefit individual breeders but is an aid to better performance in the whole Angus breed.

Since its first run, the association has gotten feedback from ranchers across the country with their observations on the EPD changes in their herds. Many call in with questions and concerns over the EPD number changes on individual animals, especially those with lower accuracy and unproven bulls, reports Stephen Miller, director of genetic research at AGI.

Miller was responsible for the testing and refining the initial models for single-step and testing results. “Those (unproven) bulls that have a lot of data, genomics doesn’t tend to have as much of an impact,” says Miller. “Single-step’s a new method, but the biggest impact is with lower-accuracy animals.”

Biggest impacts

While not all EPDs are as affected, certain traits are off their former marks as more genomic data is incorporated with the new method. “Milk is one of the traits there’s a bigger emphasis on in genomics now than in the past,” says Miller.

For example, he explains some bulls may have scored low on milk in genomics in the past, a time when it was a trait that wasn’t weighed as heavily. Now that there is more emphasis and data on this trait, it drops that animal’s EPD further.

Dry matter intake (DMI) is an example of a trait that’s seen some very positive changes. “In the past, the method we were using, our genetic trend for DMI was pretty flat, which didn’t really match the biology of the animals,” says Miller.

“If they’re getting bigger and growing faster, they’re (obviously) eating more.” He reports that with single-step, DMI is now showing a more positive trend which much better matches Angus biology.

One reason for the changes has to do with the model for the calculation and creation of EPDs. “Single-step is just a change in the methodology,” Miller stresses. “The biggest model change was around carcass weight. What single-step has allowed us to do is get a more complete model for the carcass traits.”

A big part of the system’s capability is handling more genomic values, which allow for more of them to be fitted as correlated traits. The old method lacked both the bandwidth and the simplicity to feasibly add more traits.

For example, weaning weight and fat depth were incorporated to create a positive correlation. “Now we’ve got a bigger relationship between carcass weight and growth rate,” says Miller.

Miller explains these growth and carcass traits are big parts of the dollar indexes, especially terminal indexes such as Dollar-Beef Index ($B). “What people need to realize is: We didn’t change the $B model,” he says. “Single-step doesn’t do anything with your $B directly.

What has changed is the EPDs on the animals. So single-step changes the EPDs, and the EPDs change the $B equation, and the $B itself changes.”

Why better, why now?

Gone are the days of waiting for the National Cattle Evaluation reports. Single-step is a system advanced enough to run on a weekly basis, getting large amounts of the most updated data straight into the hands of cattlemen.

But the numbers mean little if they don’t have the concrete proof to back their accuracy. Years of work on behalf of the University of Georgia and AGI have found many ways to make the system as accurate as possible even while handling large amounts of data.

This makes a big difference as compared to the past, when relying heavily on standard phenotyping raised lots of room for bias among animals.

“The animals that get genotyped are obviously not a random sample,” says Miller. “When you actually fit all the data at the same time, you have a better chance of accounting for that bias.” The association stresses the place of collecting phenotypic data remains as important as ever, as it is coupled with new genomic data. Both components are essential pieces to the strength of the method’s accuracy.

The more relatives an animal has genotyped, the more accurate the genomic data and the more accurate the EPDs. Miller hopes this will motivate more cattlemen to continue to genotype more of their animals to increase accuracy for themselves and the breed as a whole.

“Single-step is more eloquent or more sophisticated, in a way, because it actually takes into account the amount of information,” he says. “If an animal is well committed to data with a lot of relatives that are genotyped, it will reflect the accuracy of the numbers printed on that animal. That level of sophistication wasn’t in the old method.”

Changing the future

Miller hopes the introduction of the single-step method will help further the industry’s genomic and genetic progress. As the data becomes more attainable, more accurate and more proven, it raises its value and appreciation in breeding circles.

“If you’re going to sell an Angus animal with EPDs, it can be backed by genotype,” says Miller. “We keep adding more accuracy and more data; with single-step, we’ve increased the accuracy. With that, the value of genotyping goes up and up.”

He says he sees a future where genotyping becomes a standard practice in the cycle of selling and breeding registered Angus animals. “Last year, we had 110,000 genotypes come in, and there were 330,000 calves registered. If you do the math, you could say, ‘Well, only one in three are genotyped, so we’re not there yet.” On that note, Miller is happy to report the Angus Association is steadily seeing more and more genotyped animals each year.  end mark

Jaclyn Krymowski is a freelance writer based in Ohio.

Jaclyn Krymowski
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