Caninie genetics and health testing: what do i need to know

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

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