Which are healthier, purebred or mixed-breed dogs?

That question has fueled debate for years. One school of thought maintains that mixed-breed dogs are inherently healthier because they’re less prone to genetic diseases. But “less prone” doesn’t mean they can’t contract them.

Now, a new study shows that genetic testing can give owners and veterinarians a heads up on what genetic diseases a mixed-breed dog might get, depending on his DNA.

The study, “Frequency and distribution of 152 genetic disease variants in over 100,000 mixed breed and purebred dogs,” was conducted by Wisdom Health and Genoscoper Laboratories and published in the journal PLOS Genetics.

The landmark study is the first to show what genetic diseases mixed-breed dogs are likely to develop.

Given that 47% of US households reported having a mixed-breed dog in 2014 survey, the results of the study could have profound implications on the future of veterinary care.

Researchers looked at more than 100,000 dogs, making it the most comprehensive study of its kind ever attempted. That number included 83,000 mixed-breed dogs and 18,000 purebreds. The purebreds represented 330 breeds, types, and varieties. The results show that genetic testing can predict if a dog is at risk for developing certain diseases, as well as which genetic diseases certain mixed breeds are prone to develop.

Overall, the study bore out the common wisdom:

“There has been a long-standing perception that mixed-breed dogs are less disease prone than purebred dogs,” said Cindy Cole, DVM, PhD, DACVCP, general manager at Wisdom Health. “This DNA testing–based evidence shows that while mixed-breed dogs are in fact less likely than purebreds to develop the recessive disorders evaluated in the study, they may still be carriers.”

Which means that while fewer mixed-breed dogs than purebreds are affected by the most common disease-causing mutations tested, mixed-breed dogs can still develop genetic disorders.

The researchers tested all the dogs in the study for 152 genetic disease variants. Some of the genetic disease mutations tested include: progressive retinal atrophy, hyperuricosuria, collie eye anomaly, multidrug sensitivity, and von Willebrand’s disease.

Based on the 152 diseases tested, researchers found that:

• Approximately 2 out of 100 mixed-breed dogs are at risk of becoming affected and 40 out of 100 are carriers for at least one of the diseases.
• Approximately 5 out of 100 purebred dogs are at risk of becoming affected and 28 out of 100 are carriers for at least one of the diseases.

And testing for 152 diseases is just a drop in the bucket. While there are more than 400 different breeds of dogs, dogs have 619 documented genetic disorders—more than any other species. Compare that to the domestic cow, which comes in a distant second with 443. 

However, the study also indicates that the number of genetic disorders in dogs may be shrinking.

Researchers found that management of genetic disorders through the use of DNA testing and sustainable breeding practices can decrease the incidence of genetic diseases in some breeds. For instance, X-linked severe combined immunodeficiency, a mutation originally found in basset hounds, appears to have been eradicated.

As an example of how DNA testing could affect how a veterinarian might choose to treat a patient, the researchers cite the case of a female mixed-breed dog whose owner brought her in to an emergency hospital after she collapsed during play on two separate occasions. Medical staff at the hospital were initially unable to identify a cause.

But when a DNA test revealed that the dog’s ancestry included Labrador retriever, rat terrier, Siberian husky, and golden retriever, it turned out that she was genetically at risk for exercise-induced collapse as described in several retriever and sporting breeds. Armed with that information, veterinarians were able to diagnose the condition and provide informed treatment based on the DNA analysis.

“For owners, understanding for which genetic diseases their dog is at risk can help them and their veterinarians design a personalized care and wellness program for their dog," said Jonas Donner, PhD, chief scientific officer at Genoscoper and the lead author of the study. “More broadly, for veterinarians to understand which disorders are common across the overall population is extremely valuable information for the future of proactive medical care.”

More specifically, Donner said, by using DNA testing, “a veterinarian can today better explore if there are known inherited reasons for the symptoms before choosing the appropriate treatment.”

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