Are Mixed Breed Dogs Really Healthier Than Purebreds?

Mixed Breed Dogs vs Purebred Dogs

Is your dog purebred or a mutt? 

And what could that mean for his health and longevity?

Do you believe purebred dogs are more prone to genetic disorders than mixed breed dogs?

Some people claim that breeders who select for specific traits … can cause more frequent genetic disorders in purebred dogs. 

They talk about hybrid vigor in mixed breeds.

Hybrid vigor means greater health and resistance to disease. I’ll get into that in more detail in a bit. 

And I’ll tell you about a huge 15-year study at University of California-Davis (UC-Davis). The researchers studied 27,254 dogs with inherited disorders to find some answers. 

They theorized that since all domestic dogs come from three to five wolf lineages … 

… you might expect dogs’ common ancestry to create disorders common to all breeds.

So read on … the results may surprise you! And they might give you some insight into your dog’s health and longevity potential.

First, let’s talk a bit about hybrid vigor and what that means. 

What Is Hybrid Vigor?

Hybrid vigor is a term used in all kinds of breeding … not just for dogs. Even plants! It’s also called heterosis.

The dictionary definition is …

“increased vigor or superior qualities arising from the crossbreeding of genetically different plants or animals”.

So … many people believe that mixed breeds don’t express genetic disorders. 

And designer breeds … like goldendoodles, yorkipoos, puggles (the list is almost endless) are ever more popular. 

So breeders of these dogs are jumping on the hybrid vigor bandwagon. They’re all over the internet … claiming the practice of combining breeds increases hybrid vigor. 

But they’ve got it wrong. 

Because hybrid vigor doesn’t happen when you cross two breeds of dog. 

Hybrid vigor happens when you cross two different species. 

A mule is an example of a true hybrid … a mix between a horse and a donkey.  Or a “liger” … a lion and tiger. 

But a cockapoo is not a hybrid. And it doesn’t have hybrid vigor. 

In fact, when you cross two breeds, you can double up on health issues. 

This is especially likely when you have the same disease tendency in both breeds. 

Anita Oberhauer PhD was on the UC-Davis research team. Here’s what she says about the Labradoodle, for example …

…“It’s a Lab and a Poodle crossed. A Labrador has the same likelihood of having epilepsy, hip dysplasia, Addison’s disease as a Poodle. So if the sire has the ‘disease liability genes’ for any of those conditions … and the mother has the liability genes for Addison’s, epilepsy, hip dysplasia, you breed them together and the offspring will have it.”

Even Wally Conron, the man who created labradoodles in 1989 says it’s his “life’s regret.” 

The demand for these mixes means they’re bred indiscriminately.  And health issues in these designer breeds abound. 

And of course, when “mutts” happen accidentally … there’s no planning involved. So you can’t predict likely health issues.

What matters more in healthy dogs is the size of the gene pool for the breed. 

Size Of Gene Pool

In 2004 there were more than 140 AKC registered breeds. 

  • The 10 most popular breeds account for more than half of AKC registered dogs. 
  • The 100 least popular breeds were less than 15% of all registrations.

This affects the size of the gene pool. 

Some ancient breeds go back about 500 years. And they’re said to be healthier … because that means they have a larger gene pool.  

Less popular breeds have smaller gene pools.  

A breed with a smaller gene pool would be more likely to have a recessive disorder. That’s because there’s less genetic variation.

So what did researchers in the UC-Davis study find out?

The UC-Davis Study

Before this study, most researchers looked at single disorders … and their tendency in specific breeds. 

But the UC-Davis researchers wanted to explore more widely.

So they looked at the prevalence of inherited disorders in the dog population as a whole.

Dogs In The Study

The study divided the dogs into two different categoriess:

  • Purebred dogs. These included AKC-recognized breeds, AKC miscellaneous breeds and Foundation Stock Service breeds.
  • Mixed breed dogs.

They excluded non-domesticated canines like dingoes or wolves. And they viewed Pit Bulls separately. (Because it was hard to confirm their purebred status.)

Control Dogs

The control dogs came from healthy dogs at the teaching hospital during the study period. 

The researchers classified healthy dogs by …

  • Age
  • Weight
  • Sex (including whether neutered or intact)

Then they matched these dogs to each affected dog for the disorders … and randomly selected the control dogs for each disorder.

The Disorders

From 1995 to 2010, the researchers studied 27,254 dogs with inherited disorders at the University of California-Davis Veterinary Medical Teaching Hospital.

They studied 24 different disorders in five categories:

Cancers

  • Hemangiosarcoma
  • Lymphoma
  • Mast cell tumor
  • Osteosarcoma

Cardiac disorders

  • Aortic stenosis
  • Dilated cardiomyopathy
  • Hypertrophic cardiomyopathy
  • Mitral valve dysplasia
  • Patent ductus arteriosus
  • Ventricular septal defect

Endocrine disorders

  • Hyperadrenocorticism
  • Hypoadrenocorticism
  • Hypothyroidism

Orthopedic disorders

  • Elbow dysplasia
  • Hip dysplasia
  • Invertebral disk disease (IVDD)
  • Patellar luxation
  • Ruptured cranial cruciate ligament

Other

  • Atopy or allergic dermatitis
  • Bloat
  • Cataracts
  • Epilepsy
  • Lens luxation
  • Portosystemic shunt

Study Results

The theory that purebred dogs are more prone to disease doesn’t really hold up. Let’s look at some numbers.

Disorders In Both Groups

Of 24 disorders the researchers monitored … 

more than half (13) were about the same in purebred vs mixed breed dogs (matched for age, sex and body weight).

  • Hemangiosarcoma
  • Lymphoma
  • Mast cell tumor
  • Osteosarcoma
  • Hypertrophic cardiomyopathy
  • Mitral valve dysplasia
  • Patent ductus arteriosus
  • Ventricular septal defect
  • Hip dysplasia
  • Patellar luxation
  • Hypoadrenocorticism
  • Hyperadrenocorticism
  • Lens luxation

Higher In Purebreds

10 disorders were more prevalent in purebred dogs than in mixed breed dogs.

  • Aortic stenosis
  • Dilated cardiomyopathy
  • Hypothyroidism
  • Elbow dysplasia
  • IVDD
  • Atopy or allergic dermatitis
  • Bloat
  • Cataracts
  • Total epilepsy
  • Portosystemic shunt

Higher In Mixed Breeds

Every disorder was seen in the mixed-breed population. 

But in this study … only one disorder was more likely in mixed-breed dogs than purebred.

That one disorder was cranial cruciate ligament rupture. And it was significantly higher … 30%. 

The researchers didn’t really know why this might happen. It’s possible combining different physical conformations reduces the resilience of the ligaments.

Caution From The Researchers

The researchers remind us that this study evaluated dogs in a teaching hospital. That could have skewed the results because …. 

  • Breeds predisposed to certain conditions may be referred more to these hospitals. 
  • Prior studies showed purebred dog owners are more likely to spend money at a referral clinic. 

So a condition may get diagnosed at a higher rate than it would in the broader population of dogs. This would mean the study caused overrepresentation of some problems in purebred dogs. 

Nonetheless … it’s worth knowing which breeds were more prone to certain diseases.

Is Your Breed On The List?

Among the 10 genetic disorders with a significantly greater probability in purebred dogs, the top breeds with each disorder are shown below.

Some conditions are higher among very small or very large breeds.

Aortic Stenosis

  • Newfoundland (6.80%)
  • Boxer (4.49%)
  • Bull Terrier (4.10%)
  • Irish Terrier (3.13%)
  • Bouvier des Flandres (2.38%)
  • Mixed breed (0.15%)

Dilated Cardiomyopathy

  • Doberman Pinscher (7.32%)
  • Great Dane (7.30%)
  • Neapolitan Mastiff (6.52%)
  • Irish Wolfhound (6.08%)
  • Saluki (5.88%)
  • Mixed breed (0.16%)

Elbow Dysplasia

  • Bernese Mountain Dog (13.91%)
  • Newfoundland (10.28%)
  • Mastiff (6.55%)
  • Rottweiler (6.31%)
  • Anatolian Shepherd Dog (5.41%)
  • Mixed breed (0.90%)

IVDD

  • Dachshund (34.92%)
  • French Bulldog (27.06%)
  • Pekingese (20.59%)
  • Pembroke Welsh Corgi (15.11%)
  • Doberman Pinscher (12.70%)
  • Mixed breed (4.43%)

Hypothyroidism

  • Giant Schnauzer (11.45%)
  • Irish Setter (7.69%)
  • Keeshond (6.63%)
  • Bouvier des Flandres (6.55%)
  • Doberman Pinscher (6.30%)
  • Mixed breed (1.54%)

Atopy Or Allergic Dermatitis

  • West Highland White Terrier (8.58%)
  • Coonhound (8.33%)
  • Wirehaired Fox Terrier (8.16%)
  • Cairn Terrier (6.91%)
  • Tibetan Terrier (5.86%)
  • Mixed breed (1.08%)

Bloat

  • Saint Bernard (3.76%)
  • Irish Setter (3.42%)
  • Bloodhound (3.39%)
  • Great Dane (2.80%)
  • Irish Wolfhound (2.70%)
  • Mixed breed (0.20%)

Cataracts

  • Silky Terrier (22.76%)
  • Miniature Poodle (21.49%)
  • Brussels Griffon (20.51%)
  • Boston Terrier (19.61%),
  • Tibetan Terrier (18.92%)
  • Mixed breed (4.04%)

Epilepsy

  • Catahoula Leopard Dog (3.90%)
  • Beagle (3.57%)
  • Schipperke (3.42%)
  • Papillon (3.40%)
  • Standard Poodle (3.19%)
  • Mixed breed (0.91%)

Portosystemic Shunt

  • Yorkshire Terrier (10.86%)
  • Norwich Terrier (7.41%)
  • Pug (5.88%)
  • Maltese (5.87%)
  • Havanese (4.35%)
  • Mixed breed (0.35%)

Study Conclusions

These are some highlights of the resarchers’ conclusions. 

  • The theory that purebred dogs are more susceptible to inherited disease … is only true for some disorders (10 out of the 24 studied).
  • Some conditions have a clear distinction between purebred and mixed-breed dogs
  • Others show no difference.
  • Reliable genetic tests or screening … could reduce some disorders in the overall dog population.
  • Breed registry intervention could minimize selection pressures … that can contribute to a certain disorder in a breed
  • “Recently derived breeds” or breeds from similar lineages …were more susceptible to certain disorders that affect all closely related purebreds
  • Disorders with equal prevalence in purebreds or mixed breeds … seemed to be more ancient mutations that are widely spread through the dog population

The researchers noted several hypotheses about the results. They’re interesting to read … and I encourage you to read the study discussion.

And remember … for more than half the diseases studied, purebred dogs are not more susceptible

But perhaps your breed is on the list for the 10 disorders where purebred dogs are at higher risk.

In that case, this information may help you take steps to protect your dog.

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