Canine Health and Genetic Testing
Caninie Genetics and Health Testing: What do I need to know?
You don’t need a degree in genetics, or even a college course,
to understand the basics of health testing in dogs.
Every aspect of any dog’s physical being began as contributions
from it’s parent’s bodies,carried in their genetic code. As an
example, there are certain health conditions in Golden
Retrivers, Poodles and Labradors which can be passed from parent
to puppy in the genetic material. Hence are found in the hybrids
known as Goldendoodles (Golden Retriever/Poodle crosses) and
Labradoodles (Labrador Retriver/Poodle crosses). These are
called heritable (that is, “able to be inherited”) disorders. In
only one case, Von Willebrand’s Disease, do we actually know
what gene is responsible. In the case of this disease, a
laboratory can examine cells from a dog to see if the gene is
present. A dog having the gene would not be bred.
In all other instances we cannot look for a gene to tell us of
the presence of a certain disease. We have to look for evidence
of the disease itself. In the case of heritable eye diseases in
Poodles and Doodles, for example, an exam is conducted by a
veterinary opthamologist every year to determine if a disease is
developing. Dogs that show symptoms of a heritable eye disease
are eliminated from the breeding program. Other examples of
heritable diseases tested for by some Doodle breeders include
thyroid disease, some forms of heart disease, Addison’s disease,
sebaceous adenitis, hip dysplasia and diabetes.
The heritable disease found in Doodles that most people seem
familiar with is Hip Dysplasia (HD). This disease is a sort of
Degenerative Joint Disease (DJD) , with symptoms similar to
arthritis in humans. In dogs though, the heritable form of the
disease is not a disease of old age, but can develop while the
dog is still quite young and is obvious on X-rays as the hip
joint has abnormal features which are present from birth. As
with most things, the hip architecture can range from great to
horrible, with some hips in between. Two schemes are commonly
available in the US for evaluating hips. OFA screening relies on
veterinarians reading an x-ray and assigning a rank:
‘Excellent’, ‘Good’, ‘Fair’ ‘Borderline’ or ‘Dysplastic’.
Breeders who base decisions about breeding on OFA generally
agree that ‘Excellent’ and ‘Good’ rankings are fine to breed,
and also agree that ‘Borderline’ or ‘Dysplastic ‘ are not
acceptable for breeding. As with all other decisions where there
are gray areas, some breeders will breed a dog with a ‘Fair’
rank, and others will not. But this is really a judgement call
and not all breeders agree. There is a registry (www.offa.org)
that collects and reports hip assessments to assist in recording
and tracking these rankings. OFA will not certify a dogs hips
until the age of 2 years, however, so some breeders are using a
specialized x-ray technique called PennHIP testing, which can be
done as young as 4 months of age. This test results in a score
for each hip, ranging from .1 to .9, and reflects how tight the
hip joint is, and the average score varies by dog breed. Tighter
hips, that is lower scores, are less likely to develop DJD and
are desirable in any breeding dog. In my opinion, any score
under .3 is clearly breedable. Anything over .6 is clearly not
breedable. In between .3 and .6 is a gray area. Breeders who
utilize this method track the average scores for their breed,
and try to breed only dogs with average or better-than-average
scores. For example, the average hip score for Standard Poodles
is currently .5. If a Poodle were to score .42, in the middle
zone, it would be considered breedable by most because it is
better than average. However .42 would NOT be considered
breedable by most Borzoi breeders because that breed average is
..19!
Mini-Labradoodles are at risk for slightly different problems as
they are bred from Miniature Poodles instead of Standard
Poodles. For example, the incidence of hip dysplasia is so low
in the Minis that some breeders choose not to test for it. So
breeders may test for some or all of these diseases. Some
breeders do not test at all. If testing for heritable diseases
is important to you it should be among the questions you ask of
prospective breeders.
Another way breeders try to eliminate HD and other heritable
diseases from their breeding lines is to examine their dog’s
pedigrees carefully. Looking at hip assessments and other health
records of relatives (grandparents, siblings, half-siblings,
cousins, etc) and choosing breeding stock with the healthiest
background possible is all part of the picture.
One of the difficulties in trying to eliminate heritable
disorders in dogs is that most of the genes that cause the
disorders are what are termed ‘recessive’. This means they are
hidden, or masked, by other genes. A parent that does NOT show
the disease, but is carrying the gene, can pass that gene
carrying the disease to a pup. If BOTH parents happen to be
carriers and pass the genes to a pup, the pup can have TWO
defective genes and will show the disease. This is similar to 2
brown-eyed parents having a blue eyed child. Blue is recessive,
but if both parents are blue carriers, they can have a blue
-eyed child. Some heritable diseases are passed in this manner,
via a single recessive gene. Complicating this picture in the
case of HD is the fact that hip dysplasia appears to be
controlled by several genes, so predicting it’s inheritance is
even more difficult. It IS possible to have 2 parents with good
hip scores, or good hip x-rays, produce a puppy with hip
dysplasia.
In addition to testing members of a breeding pair, breeders will
gather testing information on relatives of their breeding pair.
The scores of parents, grandparents, siblings, siblings of
parents, and even puppies produced from previous litters will
all be examined. In some cases it is better to breed a dog with
slightly below average hips, if the test results for all
relatives are excellent, than to breed a dog with good hips who
has HD in it’s pedigree. So interpreting test results is no easy
task! This is true for the other heritable diseases passed as
recessive traits as well.
But Doodle breeders who test their breeding stock do the best
they can. They use their dogs test results to help make the best
pairings possible in their breeding decisions. The hope is to
reduce the number of Doodle pups born with hip dysplasia by
removing dogs from the breeding population that have clearly
substandard hips, and by following the offspring of dogs with
hip scores in the middle ranges to see if their pups remain
healthy. We do the same for all diseases that are known or
suspected to be heritable in Labradoodles and Goldendoodles
Helene Roussi raises and breeds Labradoodles and Goldendoodles
in Columbus, Ohio.