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BREEDING MAY PASS ON ORTHOPEDIC PROBLEMS IN CANINES

News Release, prepared by Kansas State University

Thursday, January 16, 1997

MANHATTAN -- For every breed of dog there is an orthopedic hereditary disease they are prone to developing, said James Roush, a doctor of veterinary medicine at Kansas State University.

Some traits are transferred through simple recessive or dominant genes while others are polygenetic, meaning they are affected by many genes, Roush said. It is difficult to control the transmittal of these polygenetic traits when selecting dogs for breeding and in fact these elusive traits are often the result of human intervention, he said.

"Some diseases and malformations develop as a chance mutation," Roush said. "But often the ones caused by partial genes result from traits we've bred for. For instance, Boston terriers and pugs are cases where we kept breeding for shorter and shorter noses, but the lower jaw stayed the same size, causing it to be overshot."

Breeding to obtain certain qualities has yielded various malformations. Basset hounds have trouble with radial closure, a disease affecting the bones of the forelimbs, because they have been bred to have short legs, and numerous types of back problems are common in dachshunds due to breeding for long torsos, Roush said.

Also, hip and elbow dysplasia, degenerative joint diseases, have become prominent problems especially in large and giant breeds because they have been bred for fast growth and large skeletal frames, he said.

Inbreeding or over-breeding animals has spawned still other diseases. Ocular and skeletal dysplasia, which causes the animal to be blind and dwarfed and is common in Labrador retrievers, is often a result of an important breeding animal which carried the trait, Roush said.

The animal is bred heavily, and three to four generations later there is inbreeding amongst the offspring which can trigger the recessive trait and thus deformity, he said.

"A lot of times a disease can be traced back to one single pedigree," Roush said. "For example, if a racing animal was the best racing animal of the time and was bred heavily but had a bad recessive trait, in eight to 10 generations it's spread entirely throughout the breed."

Other common orthopedic disorders include OCD or osteochondrosis which can affect any joint in large breed dogs; patella luxations, a knee disorder, especially in small breeds; legg-calvé-perthes, decay within the hip joint, especially in small breeds; and hemivertebra, abnormal development of the vertebrae, also common in small breeds.

Roush said the only way to hamper the genetic transfer of diseases is to inspect breeding animals carefully.

"It's very important to test animals for diseases before breeding them," Roush said. "In breeding you always want to keep the stock free of known defects if you want to maintain the quality of the breed."

Taking prospective breeding animals to a veterinarian before breeding is a good idea, he said, and doesn't cost a lot. General physical exams for pets range from $15 to $25 at the veterinary teaching medical hospital at KSU, Roush said. If the owner is interested in a specific disorder, like hip dysplasia, a radiograph can be done and sent to be analyzed by specialists for around $35 to $40, he said.

If a dog should be diagnosed with an orthopedic disorder, it can be costly to correct. Prices range from $400 to $500 to operate on a dog with OCD, to around $2,000 to replace a hip, Roush said. Mending the problem surgically does not make the animal fit for breeding.

When selecting an animal for breeding purposes, the best thing to do is to look as far back in the pedigree as possible, because at this point is impossible to test a healthy animal for potentially harmful genes, Roush said.

"There are no genetic markers for harmful genes, though genetic testing may be the wave of the future," Roush said. "A fair portion of the research going on in the United States is geared toward completely analyzing the human DNA so we can know where all of the traits are located. Perhaps in many years to come, that may transfer over to animals."

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