UW researchers help identify fatal disease in Red Angus

 Researchers in the University of Wyoming's College of Agriculture, in collaboration with others, identified a gene mutation responsible for a fatal bone disease in Red Angus cattle. The team also developed a commercially available diagnostic test for identifying carriers of the defect.

The mutation causes osteopetrosis (OS), which is commonly referred to as marble bone disease because the bones of affected calves shatter easily, like marble.

Calves are typically born 10 to 30 days premature and dead. The few calves born alive generally die within 24 hours.

One of the researchers, Shannon Swist, a UW Department of Veterinary Sciences assistant professor and a Wyoming State Veterinary Laboratory (WSVL) pathologist/veterinarian, said OS occurs in multiple species of animals, including humans, dogs, cats, horses, cattle, sheep, deer, rabbits, mice and rats.

The disease may result from acquired causes, such as infection with bovine viral diarrhea virus or canine distemper virus, Swist said, or may be caused by an inherited defect, as is the case with OS in Red Angus.

"In cattle, osteopetrosis occurs in Black and Red Angus in North America, Hereford, Simmental, Aberdeen-Angus, Holstein and other breeds," she said. "OS in Red Angus is due to a lethal genetic defect caused by a recessive mutation in a gene involved with bone remodeling during development."

Also involved in the research from the Department of Veterinary Sciences are Professor Donal O'Toole and the WSVL's chief virology technician, Jackie Cavender.

O'Toole said the disorder causes an overabundance of bone to form. When this occurs in the skulls of Red Angus calves, it compresses the brain and results in death in late gestation. It also affects the cavities of long bones such as the femur, and these bones are easily fractured.

"We first started seeing cases last year. The main focus now is encouraging producers to test all registered Red Angus for the disease and encouraging them to sell semen only from bulls that are OS-free," O'Toole said. "We worked closely with one producer in Wyoming to submit calves suspected of having the disease. Once the pathologist confirmed the diagnosis based on necropsy findings, DNA samples were taken and sent to a genetics lab. The molecular geneticists needed DNA from proven positive calves to find the defective gene."

O'Toole added, "The Red Angus Association of America (RAAA) has done an exemplary job in being open about the defect and doing what needs to be done so a test was developed for carriers. As long as producers test for the disease, carriers will be detected and quickly eliminated from the breeding population."

Larry Keenan, director of breed improvement for the Denton, Texas-based RAAA, said 4,190 Red Angus bulls, cows and calves had been tested nationally for OS by Oct. 1, and 765 were positive.

"We're expecting in the next several months the number of tested animals will increase; this is because a wider availability of testing due to new labs being approved and fall weaning," Keenan said.

Some producers are sending OS-positive animals to slaughter (there are no known risks consuming their meat), Keenan said, while others are continuing to breed these animals but are testing all of the offspring to determine whether the genetic disorder was passed on.

The RAAA has about 2,300 members, including 54 in Wyoming, with a total active cow herd of approximately 87,000 breeding animals. Keenan said the number of OS-positive animals represents a small fraction of the total number of registered Red Angus.

Keenan, though, stresses the RAAA is taking the disease seriously and is doing everything it can to help producers curb the problem.

"We have spent considerable resources educating our producers in how to identify affected calves. They will always have a short lower jaw. That's the only thing that looks abnormal," he said. "This means some producers may not have investigated a death assuming it was natural causes or a late-term abortion."

The RAAA Web page (http://redangus.org/) contains much information about OS, including details about new diagnostic tests offered by Pfizer Animal Genetics, the RAAA's genetic defect policy, a question-and-answer section, a herd genetic defect status report and a listing of approved DNA testing facilities.

Swist said, "Testing of Red Angus is underway, resulting in publicly available lists of carrier and tested-free animals posted with the cooperation of the RAAA on its Web site. Testing for carriers of the OS defect is essential to avoid the negative impact this disease has on the calf crop and preventing proliferation of the recessive gene in the Red Angus population."

In addition to the UW Department of Veterinary Sciences team, others involved in identifying the gene mutation responsible for OS and developing a diagnostic test were from the University of Illinois at Urbana-Champaign (UI), University of Nebraska-Lincoln (UN), University of Maryland, U.S. Department of Agriculture's (USDA) Roman L. Hruska U.S. Meat Animal Research Center (USMARC) in Nebraska, USDA's Henry Agaard Wallace Beltsville Agricultural Research Center in Maryland and the RAAA.

DNA testing was overseen by Jon Beever, an associate professor at UI, and Timothy Smith, a research chemist at USMARC. David Steffen, a pathologist at UN's Veterinary Diagnostic Center, is the Red Angus genetic defect consultant who worked with Swist, O'Toole and others on diagnostic work.

Swist and her colleagues will present information about the nature of the malformation and the genetic defect at the 60th annual meeting of the American College of Veterinary Pathologists this December in Monterey, Calif.

More information on this story and other research in the College of Agriculture is in the fall 2009 edition of Ag News. The online version can be accessed at www.uwyo.edu/uwexpstn/AGNEWS/fall09.pdf.

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Posted on Thursday, October 08, 2009

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