Veterinary researchers have recently published a study questioning the widely and long held assumption that mixed breed dogs are healthier than purebred dogs. The phenomenon of "hybrid vigor" was assumed to be the reason. (Hybrid vigor is a genetic theory that says mixing disparate genes by breeding very different, unrelated individuals "dilutes" the affect of any "bad" genes that may be present, lessening their impact.) This new research instead shows both purebred and mixed breed dogs to be equally susceptible to the many possible genetic disorders of the domestic dog. In this study, the oft repeated claim that purebred dogs were generally unhealthy as compared to mixed breed dogs, was found to be inaccurate. The study also shakes the notion that mixing breeds is certain to lessen the incidence of genetic disease.
The work was done at the University of California, Davis School of Veterinary Medicine and published in the Journal of the American Veterinary Medical Association this year.
The “retrospective” study involved evaluating more than 90,000 veterinary medical records of dogs seen between 1995 and 2010. Of those, 27,254 dogs presented with at least one of 24 genetic conditions under study. The results showed mixed-breed dogs to be susceptible to 13 inherited conditions including one form of cardiomyopathy, certain forms of cancer and hip dysplasia. The study found a lesser basis for the perception that purebreds are more susceptible to cataracts, another form of cardiomyopathy and thyroid dysfunction. Statistically there was little difference between both types.
Mixed-breed dogs were more likely to suffer from ruptured cranial cruciate ligament than their purebred counterparts. That condition is equivalent to anterior cruciate ligament (ACL) injury in humans, which is common in basketball players. Former Husky Rebecca Lobo suffered an ACL injury a few years ago.
The take home message from the study is that mixed breeding alone will not eliminate the most common and frequently seen genetic disorders in dogs. That is why some genetic disorders still show up in mixed breeds. The researchers explain this by pointing out that genetic mutations can independently arise multiple times and that affected dogs may share a distant ancestor.
One criticism of the study is that diseases are identified only if looked for, and purebred dogs are more commonly screened for known potential problems. Comparing how common a genetic condition is in purebred verses mixed breed dogs therefore creates a potential bias in the study. Still, the most common genetic disorders tended to be seen equally in both mixed and pure bred dogs.
