A University of California, Davis, study published in the June online edition of the Journal of the American Veterinary Medical Association has suggested that mixed-breed dogs are not always more resistant to inherited canine disorders than their purebred counterparts, the university reported in a news release.

UC Davis researchers analyzed health records from more than 90,000 purebred and mixed-breed dogs examined at the UC Davis veterinary medical teaching hospital between 1995 and 2010. The researchers then identified 27,254 of those dogs that presented with one or more of 24 specific genetic disorders.

According to researchers, analysis of the records from the 27,254 dogs revealed that:

• 13 of the 24 genetic disorders were equally prevalent in purebred and mixed-breed dogs.
• Purebred dogs suffered from 10 of the genetic disorders more often than mixed-breed dogs.
• Mixed-breeds presented with one of the disorders more frequently than purebreds.

The results indicate that "the prevalence of these genetic disorders among purebred and mixed-breed dogs depends on the specific condition," according to Anita Oberbauer, professor and chair of the Department of Animal Science at UC Davis and lead author of the study.

As an example, Oberbauer explained that mixed-breed dogs are more susceptible to cranial cruciate ligament rupture, while purebred dogs are more likely to experience elbow dysplasia and dilated cardiomyopathy.

The study also shed more light on how breed lineage can affect a dog's chances of having certain genetic disorders. According to researchers, separate breeds stemming from the same common ancestor are more likely to have certain genetic disorders. One example raised by researchers is that four of the top five breeds most susceptible to elbow dysplasia were the Bernese mountain dog, Newfoundland, mastiff and Rottweiler, which all descended from mastiff-like heritage.

Breeds that are more recently derived are also more susceptible to genetic disorders, researchers said.

The study also found that certain genetic disorders are shared equally between purebred dogs and mixed-breed dogs because some ancient gene mutations have become widely dispersed throughout the dog population. These include hip dysplasia, hypertrophic cardiomyopathy, and all of the tumor-causing cancers, researchers said.

Oberbauer said she is optimistic that the study's findings might play a part in the effort to prevent and treat genetic disorders in dogs and possibly humans.

"Results from this study give us insight into how dog breeding practices might be modified to reduce the prevalence of certain genetic disorders," she said.