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,
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
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
Copyright © January 1997.
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