Testing expands understanding of DD gene

Jon Beever, University of Illinois professor of genetics, says the defect was named for the varying body part duplications it can cause.

Wendy Sweeter

“These calves that have outward signs of the condition have duplicated appendages for a number of different body parts,” he says. “Basically, what happens is there’s a population of cells that early in development is quite potent where they can develop into lots of things given the proper stimulus.”

Beever says in embryonic development during the closure of the neurotube in animals that carry the defect, cells escape from the neurotube. Wherever those cells end up migrating, they can detect localized signals from surrounding cells and develop whatever that signal tells them.

Those could include duplicated heads, faces, spinal cords, tails and legs.

The recessive genetic disorder is simply inherited. Retallick says they see more producers testing for defect carriers during the fall when producers are weaning calves through bull sale season.

“While we don’t require them to test for DD to register those animals, they like to clean them up for their commercial cow-calf buyers so they don’t have to worry about trying to track which animals they’re breeding those DD animals to,” she says. “A lot of our seedstock guys will be proactive just so they’re servicing their commercial customers to the best of their ability.”

For producers who want their animals tested for DD, they need to obtain a blood or hair card from AGI. They then collect the sample themselves and send it in to AGI with their lab-testing preference of Zoetis or GeneSeek.

The whole process takes about three weeks. Cost per test is $22 for a stand-alone test. Retallick says many producers choose to do the test and an add-on genomic trait test.

Beever and Retallick say breeders normally test their oldest animals to hopefully clear progeny.

“If they can get that one clear, that can clear the potential progeny that can be a carrier for that genetic condition,” Retallick says.

When the mutation was showing up in the U.S. three years ago, Beever and other geneticists went back as far as they could to obtain DNA from the oldest animal that was a potential common ancestor. In the case of DD, the defect had appeared in a bull prior to 1978. The oldest bull they could find that most commonly showed up in animals that showed the defect came from a bull born in 1990.

Once they find the oldest common animal, they genotype them and find out if they have the mutation.

“If they do, we give that to the breed association, and the breed association has these tools that will calculate risk – and given that risk you may or may not want to test your animal for this condition,” Beever says.

Retallick and Beever say besides DD, they have seen another defect called osteopetrosis, or marble bone disease, show up in the Angus breed. Beever says it is an old defect that has been known about since the 1960s.

“We thought it was bred out of our population. There’s been an affected animal reported to us this spring. That is one that is a lethal carrier, so we require people to test for registration purposes,” Retallick says.

Beever says in the last 15 months, the American Simmental Association has seen some calves born with very light-colored eyes. Beever says that trait goes back to the late 1970s Angus pedigrees.

Retallick encourages Angus breeders to test their animals to supply their commercial buyers with the most information possible for them to make breeding decisions.

“We also encourage genomic trait testing to get genomically enhanced EPDs. That provided with the American Angus Association database, pedigree information and performance information that we get to our breeders really is the most accurate prediction of that animal’s genetic merit as a parent that we have today,” Retallick says.

“I feel the commercial industry is starting to demand more and more information because it truly is a risk assessment tool for them.”