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Clearing up misconceptions about EPDs

Progressive Cattleman Associate Editor Carrie Veselka Published on 23 April 2018
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What exactly are expected progeny differences (EPDs) and what information do they really offer producers? Genetic specialists Alison Van Eenennam from the University of California – Davis and Matt Spangler from the University of Nebraska – Lincoln teamed up for the first of four webinars focused on beef genetics that were sponsored by the National Cattlemen’s Beef Association and eBEEF team.

“An EPD is an estimate of the expected genetic merit of an animal,” Van Eenennam explained. “It functions as the pedigree, individual performance record and progeny performance record. EPDs are the best estimate we have of how a bull or cow’s future progeny will perform, on average, compared to another bull or cow, or the breed average for a given trait.”

Van Eenennam said selection based on EPDs is five to nine times more accurate than selection based on index performance and ratios. “Many producers mistakenly place emphasis on raw measurements or adjusted phenotypes, rather than the EPDs, but the EPD has already got that information incorporated,” she said.

She said selection based on phenotypes such as actual weight or corrected weight is not an accurate measurement because environmental influences like herd, year, season and management are factored in. “That can really impact that number, but it’s not something that is transmitted to the progeny,” she said. “The overall goal is to match your genetics with the environment and what your breeding objective and goals are, so bigger – not always better.”

The debate on calving ease

Van Eenennam said selecting for low birthweight is a bad idea if complication-free, unassisted births are the end goal. “Really, what you’re trying to do is improve the percentage of your herd that has unassisted births, and that’s what Calving Ease Direct is a measurement of,” she said. “It’s related to the level of assistance needed during a calving event.”

Van Eenennam said while selection to decrease birthweight is a good attempt to reduce calving problems, it doesn’t have a direct revenue or cost associated with it that goes back to the operation. “It’s really the unassisted births that is the important, economically relevant trait here,” she said.

Van Eenennam said birthweight only explains 36 to 64 percent of the genetic variation associated with the Calving Ease Direct EPD (CED); there are other things that contribute to the likelihood of an unassisted birth that are not accounted for in the predicted weight of the calf, so birthweight is only an indicator trait for CED.

“The bottom line there,” she said, “is to focus on CED if you’re concerned about increasing the levels of unassisted births on your operation.”

Sharing information on EPDs

Spangler said that if an animal does not have a phenotypic record for a trait, it is still possible to produce an EPD for that trait for that animal through two ways: sharing information and correlating information.

Spangler said tools like DNA markers help to establish the relationship between animals as close as parent to offspring or two of the same breed. “These relationships allow phenotypes that may be collected on one animal to help inform the genetic value or EPD on another animal,” he said.

Spangler used parent/offspring traits and sex-limited traits as an example. “There’s no way a bull is ever going to have a heifer pregnancy record himself, but he can have an EPD for heifer pregnancy, and that is because of his half-sibling females and certainly his daughters that become pregnant as heifers or fail as heifers,” Spangler said. “Those phenotypes inform his EPD.”

He said correlation is another good way to get an informed EPD because many traits have at least some degree of genetic correlation between them. For example, early growth traits like birthweight and weaning weight can be correlated to calculate a later growth EPD like yearling weight. “We can get an EPD for yearling weight with reasonable accuracy by just having birthweight and weaning weight records because they’re correlated to the trait of yearling weight,” he said.

Uniformity: Yes or no?

Spangler also tackled the myth that bulls with a higher EPD accuracy will have a more uniform group of offspring.

“Accuracy is not the same thing as precision,” he said. “Accuracy of a bull’s EPD does not tell us anything about how uniform his offspring group is going to be. Accuracy gives us a measure of how closely related the EPD or prediction of their genetic merit is to their true progeny difference – the true genetic merit that is apparent.”

Spangler said focusing on desired traits is key to getting the genetic qualities you want in your herd. “If you want to increase the uniformity of your calf crop and you’re using several different bulls, the best way to increase uniformity is to select those bulls to be very similar in terms of the EPDs for the traits that you’re interested in,” he said. “That’s the best way to increase uniformity genetically.”

Spangler also reminded producers that genetic uniformity in a calf crop might be overrated. “If all the offspring were the same, you wouldn’t be able to make any genetic change.”  end mark

Carrie Veselka
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PHOTO: EPDs work if you understand the information. Staff photo.