By Helene Roussi
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 contributionsfrom it's parent's bodies,carried in their genetic code. As anexample, there are certain health conditions in GoldenRetrivers, Poodles and Labradors which can be passed from parentto puppy in the genetic material. Hence are found in the hybridsknown as Goldendoodles (Golden Retriever/Poodle crosses) andLabradoodles (Labrador Retriver/Poodle crosses). These arecalled heritable (that is, "able to be inherited") disorders. Inonly one case, Von Willebrand's Disease, do we actually knowwhat gene is responsible. In the case of this disease, alaboratory can examine cells from a dog to see if the gene ispresent. A dog having the gene would not be bred.
In all other instances we cannot look for a gene to tell us ofthe presence of a certain disease. We have to look for evidenceof the disease itself. In the case of heritable eye diseases inPoodles and Doodles, for example, an exam is conducted by aveterinary opthamologist every year to determine if a disease isdeveloping. Dogs that show symptoms of a heritable eye diseaseare eliminated from the breeding program. Other examples ofheritable diseases tested for by some Doodle breeders includethyroid disease, some forms of heart disease, Addison's disease,sebaceous adenitis, hip dysplasia and diabetes.
The heritable disease found in Doodles that most people seemfamiliar with is Hip Dysplasia (HD). This disease is a sort ofDegenerative Joint Disease (DJD) , with symptoms similar toarthritis in humans. In dogs though, the heritable form of thedisease is not a disease of old age, but can develop while thedog is still quite young and is obvious on X-rays as the hipjoint has abnormal features which are present from birth. Aswith most things, the hip architecture can range from great tohorrible, with some hips in between. Two schemes are commonlyavailable in the US for evaluating hips. OFA screening relies onveterinarians reading an x-ray and assigning a rank:'Excellent', 'Good', 'Fair' 'Borderline' or 'Dysplastic'.Breeders who base decisions about breeding on OFA generallyagree that 'Excellent' and 'Good' rankings are fine to breed,and also agree that 'Borderline' or 'Dysplastic ' are notacceptable for breeding. As with all other decisions where thereare gray areas, some breeders will breed a dog with a 'Fair'rank, and others will not. But this is really a judgement calland not all breeders agree. There is a registry (www.offa.org)that collects and reports hip assessments to assist in recordingand tracking these rankings. OFA will not certify a dogs hipsuntil the age of 2 years, however, so some breeders are using aspecialized x-ray technique called PennHIP testing, which can bedone as young as 4 months of age. This test results in a scorefor each hip, ranging from .1 to .9, and reflects how tight thehip joint is, and the average score varies by dog breed. Tighterhips, that is lower scores, are less likely to develop DJD andare desirable in any breeding dog. In my opinion, any scoreunder .3 is clearly breedable. Anything over .6 is clearly notbreedable. In between .3 and .6 is a gray area. Breeders whoutilize this method track the average scores for their breed,and try to breed only dogs with average or better-than-averagescores. For example, the average hip score for Standard Poodlesis currently .5. If a Poodle were to score .42, in the middlezone, it would be considered breedable by most because it isbetter than average. However .42 would NOT be consideredbreedable by most Borzoi breeders because that breed average is..19!
Mini-Labradoodles are at risk for slightly different problems asthey are bred from Miniature Poodles instead of StandardPoodles. For example, the incidence of hip dysplasia is so lowin the Minis that some breeders choose not to test for it. Sobreeders may test for some or all of these diseases. Somebreeders do not test at all. If testing for heritable diseasesis important to you it should be among the questions you ask ofprospective breeders.
Another way breeders try to eliminate HD and other heritablediseases from their breeding lines is to examine their dog'spedigrees carefully. Looking at hip assessments and other healthrecords of relatives (grandparents, siblings, half-siblings,cousins, etc) and choosing breeding stock with the healthiestbackground possible is all part of the picture.
One of the difficulties in trying to eliminate heritabledisorders in dogs is that most of the genes that cause thedisorders are what are termed 'recessive'. This means they arehidden, or masked, by other genes. A parent that does NOT showthe disease, but is carrying the gene, can pass that genecarrying the disease to a pup. If BOTH parents happen to becarriers and pass the genes to a pup, the pup can have TWOdefective genes and will show the disease. This is similar to 2brown-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 thecase of HD is the fact that hip dysplasia appears to becontrolled by several genes, so predicting it's inheritance iseven more difficult. It IS possible to have 2 parents with goodhip scores, or good hip x-rays, produce a puppy with hipdysplasia.
In addition to testing members of a breeding pair, breeders willgather testing information on relatives of their breeding pair.The scores of parents, grandparents, siblings, siblings ofparents, and even puppies produced from previous litters willall be examined. In some cases it is better to breed a dog withslightly below average hips, if the test results for allrelatives are excellent, than to breed a dog with good hips whohas HD in it's pedigree. So interpreting test results is no easytask! This is true for the other heritable diseases passed asrecessive traits as well.
But Doodle breeders who test their breeding stock do the bestthey can. They use their dogs test results to help make the bestpairings possible in their breeding decisions. The hope is toreduce the number of Doodle pups born with hip dysplasia byremoving dogs from the breeding population that have clearlysubstandard hips, and by following the offspring of dogs withhip scores in the middle ranges to see if their pups remainhealthy. We do the same for all diseases that are known orsuspected to be heritable in Labradoodles and Goldendoodles
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