What This 90,000-Dog Study Reveals About Purebred Versus Mixed Breed Health

Analysis by Dr. Karen Shaw Becker

are mutts healthier

Story at-a-glance -

  • Many people, including some veterinarians, believe mixed breed and “designer” dogs tend to be healthier than purebreds
  • Other veterinarians and the results of a 2013 university study suggest mixed breeds don't necessarily have an advantage when it comes to genetic disorders
  • According to the study, the prevalence of 13 of 24 genetic disorders was about the same for mixed breeds and purebreds
  • The field of nutrigenomics studies the effect of nutrition on the genome, and at some point in the future, we’ll be able to influence gene expression through personalized nutrition plans
  • It can be helpful for pet parents to learn their mixed breed dog’s ancestry and health predisposition, and work with an integrative veterinarian to prevent or effectively manage inherited diseases

Are mixed breed dogs healthier than purebreds? The answer depends on who you ask. But before we go further, let’s define “purebred.” In the U.S., a dog is considered a pedigreed purebred if she or he:

  • Has papers proving mom and dad and all his or her ancestors are of the same breed
  • Is registered with the American Kennel Club (AKC)

Purebred dogs are the result of selective breeding by humans. So are hybrid or “designer” dogs, which despite their often-high price tags, aren’t technically purebreds. Hybrids are initially created by breeding two or more purebred dogs. For example, Goldendoodles and Labradoodles, two very popular hybrids, were initially created by breeding Poodles with either golden or Labrador retrievers.

Some breeders have gone on to breed purebred-to-hybrid (e.g., a golden retriever to a Goldendoodle) and hybrid-to-hybrid (e.g., a Doodle to a Doodle), creating second or third- or fourth-generation hybrids. This practice is highly controversial in the dog world, for lots of reasons.

Mixed breed dogs, in contrast, are the offspring of dogs of different breeds and breed mixes, and humans may, but usually don’t have a hand in their creation. Often their ancestry isn’t known, and DNA testing can reveal a wide and often improbable range of breeds in their lineage.

It Just Makes Sense That Mutts Are Healthier Than Purebreds — or Does It?

Now back to the question of whether mixed breeds are healthier than purebreds. One of the reasons for this belief is that when two or more breeds are blended together in one dog, it can be reasonably assumed there’s less risk the dog will inherit breed-specific diseases.

The idea that mutts are healthier makes sense when you consider the terrible breeding practices of puppy mill operators and many AKC-associated breeders as well.

Sadly, in the world of puppies-for-profit and pedigreed dogs, there is often a single-minded focus on breeding animals for certain physical characteristics — even when those characteristics cause lifelong suffering — and little to no attention paid to selecting for health and longevity.

With that said, according to what many veterinarians see in their practices,1 as well as the results of a 15-year study of veterinary cases at the University of California, Davis, mixed breeds don't necessarily have an advantage when it comes to genetic disorders.2

Certain Genetic Disorders Are Equally Represented in Both Purebreds and Mixed Breeds

The UC Davis researchers analyzed the records of over 90,000 purebred and mixed breed dogs that had been patients at the university’s veterinary medical teaching hospital between 1995 and 2010. Designer dogs were included in the study, since crossbreeding is presumed to reduce or eliminate genetic disorders like hypothyroidism, epilepsy, hip dysplasia and cancer.

The research team found over 27,000 records that involved dogs with at least one of 24 genetic disorders, including various types of cancers, heart disease, endocrine system dysfunction, orthopedic conditions, allergies, bloat, cataracts, eye lens problems, epilepsy and liver disease.

According to their study results, the prevalence of 13 of the 24 genetic disorders was about the same for purebreds as mixed breeds. Some of those disorders were hip dysplasia, hyper- and hypoadrenocorticism (Cushing’s and Addison’s, respectively), cancers, lens luxation and patellar luxation (floating kneecap).

Ten conditions were found more frequently among purebred dogs, including dilated cardiomyopathy, elbow dysplasia, cataracts and hypothyroidism. One disorder was actually more common in mixed breeds — cranial cruciate ligament (CCL) disease.

“Overall, the study showed that the prevalence of these genetic disorders among purebred and mixed-breed dogs depends on the specific condition," animal physiologist Anita Oberbauer, Ph.D., professor and chair of the Department of Animal Science at UC Davis and lead author of the study said in a university press release.3 The UC Davis study data also suggests breeds that share a similar lineage are more prone to certain inherited disorders:

“… [F]our of the top five breeds affected with elbow dysplasia were the Bernese mountain dog, Newfoundland, mastiff and Rottweiler — all from the mastiff-like lineage. This suggests that these breeds share gene mutations for elbow dysplasia because they were descended from a common ancestor.”

The flip side of the coin is disorders that occur in both mixed breeds and purebreds seem to originate from well-established gene mutations that have spread throughout the dog population. These disorders include hip dysplasia, tumor-causing cancers and hypertrophic cardiomyopathy.

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Nutrition and Genetics

It’s very important to keep in mind that just because a certain disorder is inherited in certain breeds, it doesn’t mean your dog of that breed is fated to acquire that condition. As I mentioned just above, there are steps we can take to help prevent your pet from acquiring diseases to which he may be predisposed, and there are ways to successfully treat or effectively manage existing genetic conditions.

For example, nutrigenomics is an emerging scientific concept that holds that the nutrition we need as individuals (both humans and animals) depends on our genetic makeup. Our genes and their expression are controlled by individual nutrients, which means we need personalized functional nutrition.

It’s important to understand how the nutrients we feed our pets will affect their genes, and therefore, their health and longevity. And in fact, if we know which nutrients are essential for individual pets (and people), we can impact longevity, reduce the risk of chronic disease and heal from illness much more rapidly.

Nutrigenomics studies the effect of nutrition on the genome. The genome is everything to do with the body — how it functions metabolically and genetically. The genes are only a small part of the genome, about 2 percent. The other 98 percent has nothing to do with the genes, but with how the body controls what our genes do.

Every individual has a unique molecular dietary signature that determines which nutrients that individual should eat in order to thrive. As veterinarians and pet parents, we can exert some control. For example, if your dog is a breed genetically predisposed to a certain health problem, through nutrition we can suppress certain genes so they don’t express themselves, or encourage other genes to do the opposite.

For more information on this exciting field of research, I recommend a book co-written by Dr. Jean Dodds, “Canine Nutrigenomics: The New Science of Feeding Your Dog for Optimum Health.”

If You’re Looking for More Info on Your Dog’s Breed(s)

If you're interested in learning more about inherited diseases in dogs, there are a couple of online resources you may find useful:

  • The Canine Inherited Disorders Database (CIDD) is a good resource for dog guardians with a pet diagnosed with an inherited disease, and prospective dog parents who want to learn about the inherited conditions of certain breeds.
  • The Inherited Diseases in Dogs (IDID) database is provided by the University of Cambridge Veterinary School, and users can search by selecting a breed or genetic anomaly (inherited disorder), or by typing in a keyword. This database also contains references to peer-reviewed scientific literature for further research.

There are also now DNA test kits available that provide not just breed identification, but health and genetic traits as well. Two of these are the Embark Breed & Ancestry Identification, Trait & Health Detection Dog DNA Test Kit and the Wisdom Panel Health Breed & Health Identification Dog DNA Test Kit.

If you purchase one of these kits, I strongly encourage you to review the results with your veterinarian, especially if there’s anything you feel is concerning. It can be helpful for pet parents to be aware of the disorders that are common in their dog's breed(s), because in integrative veterinary medicine in particular, there are steps we can take to prevent or slow the progression of disease.

When an inherited disorder can't be prevented or appears suddenly, if you know ahead of time what to look for and seek immediate veterinary care, your dog often has a much better outcome.