Scientists confident in Angus gene mutation identification
Researchers hope to have a commercial test by December that Angus producers can use to identify the recessive gene that causes Arthrogryposis Multiplex (AM), or Curly Calf Syndrome.
David Steffen, DVM, PhD at the University of Nebraska/Lincoln, said the cooperative way producers have responded to requests for samples of calves born with the genetic defect have helped speed research and identify the cause of the disease, which was identified in the Angus breed in August 2008.
“We’re confident that we know what the mutation is and the gene involved,” Dr. Steffen said. “The deletion in the gene in relation to the known function of the gene is consistent with the abnormal morphology we’re seeing in the calves. It does look like a recessive trait.”
While the scientists are still accepting samples, they are no longer aggressively seeking samples for their research.
“If people want to submit a sample for diagnostic purposes, they can certainly do that,” Dr. Steffen said.
On Nov. 3, 2008, the American Angus Association released a statement noting that Dr. Jon Beever of the University of Illinois, who has been working to develop a test that identified the recessive gene in sires, had worked with A.I. organizations to request semen samples to be used in his research. Although Dr. Beever did not consider his test to be “optimal,” it was used to develop a list of sires carrying the probability of passing the recessive gene to progeny.
The registration numbers and results for those animals tested are listed on AAA’s site (www.angus.org). The information includes the disclaimer noting that the preliminary test Dr. Beever used has not been validated. For that reason, the AAA will not alter or amend any registration of performance pedigree certificates until fully validated results can be obtained.
Don Laughlin, Director of Member Services for the American Angus Association, said Dr. Beever has completed thorough research and testing, which includes some highly used registered Angus sires, and the results of the tests are listed on AAA’s website. Test results are coded AMF, which indicates the animal is free of the mutation; AMC to indicate that they carry the mutation; and AMA, meaning the animal is affected by the mutation. A full explanation of the codes is available on the website.
“The mutation was found in the maternal ancestor of Precision 1680,” Laughlin says. “We are hopeful, and I emphasize hopeful, that we’ll have a commercial test available beween December 1 and 15 so producers can begin testing their cattle. We don’t have a lab identified yet, and the lab will have to indicate how DNA samples will be captured.”
Information regarding the commercial test and how producers can obtain it will be posted on the AAA website as it becomes available. Laughlin noted that producers should review their pedigrees as soon as possible to determine whether or not their cattle need to be tested.
“Unless your pedigrees go back to one of the identified carriers, which are listed on the website, your cattle won’t need to be tested,” he said.
The AAA has begun identifying the genetic mutation as AM in order to avoid confusing it with the Curly Calf disease in Australia that is caused by a virus and not a genetic mutation.
GAR Precision 1680, a sire that is listed in more than 40,000 registrations, was initially linked to the genetic mutation. The bull came from Gardiner Angus Ranch in Ashland, KS. While Precision 1680 is one of the sires known to carry the genetic defect, Dr. Steffen noted that the mutation probably existed for many generations at low levels.
“It was only the excellence of this sire in growth and quality traits that created a high impact on the population that created a circumstance where we could recognize the disease and distinguish it from environmental agents that can cause crooked or curly calves,” says Dr. Steffen. “The term ‘founder effect’ is used to describe a population change that occurs by passing thru a genetic bottleneck. Historically this was used to describe population changes occurring due to continental drift, catastrophic near extinction events that affect natural populations. In the case of the cattle industry, these events occur due to reproductive technologies and the ability for a limited number of sires and dams to have a large impact on the entire breed population. Most of these impacts have been to our advantage.”
Dr. Steffen expects that producers will see more cases of AM in the Spring 2009 calf crop, but believes the occurrence will rapidly decrease after that. In his work as director of the Cattle Congenital Disease Program at UNL, Dr. Steffen said the incidence of aberration is present in nearly every breed of cattle.
“We have an emerging problem in Holsteins that we’re examining right now,” he said. “Over the last couple of years we identified tibial hemimelia in Shorthorns, a genetic disease. We’ve also identified pulmonary hyperplasia in the Maine Anjou breed.”
Dr. Steffen noted that beef producers who see abnormalities should contact their breed association and/or his office to report unusual birth defects. Genetic problems can often be identified and managed if information from across the nation is funneled through a central location. Most often mutations are present at low frequencies early on in the population so individual events in isolated geographic locations are erroneously dismissed as unimportant. Only when calves from a wide geographic area examined at one site with data on parentage are patterns recognized or genetics eliminated as a cause.
“Most breed associations are fairly progressive in addressing this kind of issue,” says Dr. Steffen. “If a producer has concerns about how their information is handled, they can always contact our office and we will investigate their problem. It’s good to have a veterinarian review abnormalities, but they won’t have the diagnostic tools that are available to us. They probably won’t have knowledge of reports of other similar irregularities. Plant toxins and viruses can be the cause of birth defects, but investigation of each case is the only way to determine that cause.”
Dr. Steffen recommends that producers capture photos of abnormalities and make contacts while the calf is still available. Breeders can preserve carcass samples by freezing them in order to assist the investigation if contacts cannot be made immediately.
“I’ve had phone conversations with producers and heard a description of what they are seeing, but when I get their photos or see the sample they send in, it’s often quite different from what I envisioned from the conversation,” he said. “Photos are very helpful, but tissue samples are necessary for complete investigation of an incident.”
Identifying the root cause of abnormalities in cattle that are pasture bred or aren’t registered is difficult due to the uncertain gene pool involved. Dr. Steffen recommends that purebred breeders who at least have the sire’s pedigree make every effort to report any oddity or deviation they see in their herd.
“If they at least know the sire, we want to be aggressive in investigating these kinds of things,” he said. “You have to know the ancestors in order to draw any valid conclusions about potential inheritance of new diseases. The morphology can be used to diagnose known conditions in the absence of breeding information so each case needs to be considered independently.”
Both Dr. Steffen and Laughlin believe the issue will rapidly come under control following the birth of the 2009 calf crop.
“The list of affected sires is available now and that will allow producers to manage the recessive gene trait,” Dr. Steffen said. “I would expect to see very few AM births in the future.”
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