Just as DNA testing can help promote production positive traits within a herd, it also can help producers make the right mating decisions and avoid genetic abnormalities.

Developmental Duplication (DD), or polymelia, is a recently identified genetic condition in Angus cattle. The condition results in extra limbs emerging from the back, shoulder or poll, says David Steffen, Ph.D., DVM, professor at the University of Nebraska-Lincoln.

Dr. Steffen cautions that not all extra limbs are related to this specific condition. However, the classification of DD as a genetic abnormality is a new discovery for beef geneticists. Previously, all extra limbs were thought to be part of an incomplete twinning process. Animal scientists in Australia recognized this particular phenotype as a heritable problem in an Angus herd.

As a simple recessive condition, both the sire and dam must be carriers of the DD gene. Even if two carriers are mated, DD is thought to also result in early embryonic loss and open females—meaning the producer or veterinarian may never know the condition is present without genetic testing.

Early embryonic loss is one possible reason DD was not identified as readily as conditions like Arthrogryposis Multiplex (AM) or Neuropathic Hydrocephalus (NH) even though DD is estimated to be similar in scope.

“Both parents have to be carriers,” Dr. Steffen says. “Fortunately a fairly small percentage of the sires in AI service seem to have been carriers. Then, it’s not going to be expressed if those carrier bulls aren’t crossed with animals that are carriers. Even if you do make that mating, there is only a one in four chance of getting a combination to express the disease and some of those could show up as infertility. So these abnormal genes can be spread covertly for some time.”

A test for DD is already available and may be purchased alone or paired with the GeneSeek® Genomic Profiler or the Zoetis HD 50K for Angus. Producers can use archived samples or submit new samples through Angus Genetics Inc.SM

“The bottom line is DD is simple recessive, so even if I have a prevalence of carriers in my cow herd, as long as I am using bulls clean for this particular condition, I’m never going to experience any problems,” Bowman says. “This type of condition is expressed in different species and is not unique to Angus cattle. It’s out there, but it’s something we have wide enough resources and reach in the population that we are able to use the science and technology to identify.”

The American Angus Association policy on DD does not require testing as a precondition of continued or prospective registration. The association encourages producers and veterinarians to report any incidence to the association.

“We take the responsibility of providing our industry, and the commercial producer using Angus genetics, seriously and want to provide them genetics they can use with confidence in their herds,” Bowman says. “The economic implications of DD may not be as great as other things they deal with on a daily basis like calving ease, pinkeye or having cattle struck by lightning. There are a lot of things that are going to have a bigger impact on their herd. This is another piece of information.”

Bowman notes the industry’s approach to dealing with genetic abnormalities changed drastically since the 1960s and 1970s where entire lines may have been eliminated. Today, producers can make tailored mating decisions and help retain performance traits they worked so hard to achieve.

“There is a reason Angus genetics are prevalent,” Bowman says. “They make a positive impact in the economics of beef production.”

Communication and genetic testing improved the industry’s ability to identify abnormalities in herds. DD should be easily manageable for most purebred and commercial herds in the country, Dr. Steffen notes.

“Even ten years ago, it might have taken a long time to figure out what was going on,” Dr. Steffen says. “Today, it’s not nearly as threatening to the breeders. Testing is a big thing upfront for the first year or two. Then things have been traditionally cleaned up once we get the main seedstock bulls identified or tested free for carriers. That’s the advantage of testing, knowing the status of animals so we can retain the good traits and manage around a bad gene.”