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Bone disease in cattle
A disease not seen in cattle for more than 50 years is rearing its ugly head once again. Marble bone disease, also known as osteopetrosis, is a bone disorder that affects not only humans but also cattle and other animals.
It is characterized by overly dense yet brittle bones that shatter easily. Calves that suffer from the mutation have deformed skulls, receding jaws, and protruding tongues. Typically, they are stillborn or die within 24 hours of birth.
“Calves have to inherit the mutation from both parents,” says Tim Smith, a chemist in the Genetics and Breeding Research Unit at the Agricultural Research Service's (ARS) Roman L. Hruska U.S. Meat Animal Research Center (USMARC) at Clay Center, Nebraska.
When it struck Black Angus cattle in the 1960s, producers culled animals in an attempt to rid their herds of the mutation.
When the same disorder resurfaced three years ago in Red Angus cattle, scientists knew there had to be a better option that wouldn't be so costly to producers.
“With a recent case in the Northern Plains, there was a great deal of concern because the breed's most popular bull was related to some of the animals that had produced osteopetrosis-affected calves,” says Smith.
Because a number of calves were indirectly linked to the bull, breeders wanted to ensure they weren't continuously putting the DNA for the disease back into their herds.
DNA test developed
To identify the gene mutation responsible for the disorder, scientists at the ARS USMARC and the Henry A. Wallace Beltsville Agricultural Research Center (BARC) in Beltsville, Maryland, collaborated with several university and Red Angus Association of America (RAAA) partners.
Once identified, the ultimate goal of the group was to stop the disease from spreading by developing a DNA diagnostic test that identified carriers of osteopetrosis.
In calves affected with osteopetrosis, researchers found that some of the SLC4A2, a gene necessary for proper osteoclast maintenance and function, had been deleted. Osteoclastics are types of cells responsible for breaking down old bone during bone development and remodeling.
“After more than 50 years, marble bone disease resurfaces in Red Angus cattle.”
While the cattle study was taking place, other scientists were studying bone development in mice. They created a similar mutation in SLC4A2 to find out the function of the gene. It was determined to cause the same marble bone disease phenotype, which confirmed that the exact same gene in mice was responsible for the osteopetrosis mutation in Red Angus.
As a result, scientists were able to develop a PCR (polymerase chain reaction) test and make it available to breeders in less than a year, which was provided through RAAA. The test has been widely used and is required for registration of most Red Angus cattle.
Breeders now have a test they can use to manage the defect, identify cattle that may be carriers, and make decisions on whether an animal's other traits make it valuable enough to continue using for breeding, notes Smith.
By having this test available, the bone disease can be eliminated from the herd without sacrificing other genetic progress made during the development of that breed.
Agricultural Research Service www.nps.ars.usda.gov