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who is healthiest? dr. ernie ward discusses pedigrees and muttigrees

For my entire veterinary career I’ve been working under the assumption that mixed breed dogs were healthier than their pure-bred cousins. We were taught that since many hereditary genes required both parents to carry the trait, the chances of a mutt acquiring some unusual genetic defect were much less than a highborn counterpart.  New research has veterinarians reconsidering questioning that hypothesis.

Researchers from the veterinary school of the University of California, Davis evaluated the medical records of over 90,000 dogs seen from 1995 to 2010. In a published report in the Journal of the American Veterinary Medical Association, they found over 27,000 dogs with at least one of 24 genetic conditions. That’s where the study gets interesting.

Prevailing wisdom would’ve predicted that the majority of these genetic diseases would be seen in pure breed dogs. Labrador retrievers would develop hip dysplasia; Rottweilers would have bone cancer; Boxers would suffer from lymphoma. This isn’t what the data proved.

What the research demonstrated was that mixed and pure breed dogs had almost the same risk of developing many of the common genetic diseases. These inherited diseases include:

  • Hypertrophic cardiomyopathy
  • Mitral valve dysplasia
  • Patent ductus arteriosus (PDA)
  • Ventricular septal defects of the heart
  • Lymphoma
  • Osteosarcoma
  • Hemangiosarcoma
  • Mast cell tumor
  • Hip dysplasia
  • Patellar luxation
  • Hyperadrenocorticism (Cushing’s disease)
  • Epilepsy

Some diseases were found to be more prevalent in pure breeds. They include:

  • Aortic stenosis
  • Atopy or allergic dermatitis
  • Bloat
  • Cataracts
  • Dilated cardiomyopathy
  • Elbow dysplasia
  • Hypothyroidism
  • Intervertebral disk disease
  • Portosystemic shunt

One of the more interesting findings was that one of the most common leg injuries in dogs, ruptured cranial cruciate ligament, was more common in mixed-breed dogs.

It makes sense once you think about it. The diseases that are recessive genetic traits will be more common in pure-breed lines. This reinforces the importance of careful and selective breeding practices.  For many other genetic diseases, it’s more complex than simply having a mother and father with the genetic traits. That’s why we expect to see some of these diseases no matter what the lineage. But there’s an even more important message this information carries for veterinarians and pet parents.

As veterinarians we’re trained to look for certain diseases in specific breeds. What this research tells me is I need to broaden my search for diseases beyond the typical or expected breeds to my mixed-breed patients. Pet parents need to move away from the belief that having a mutt means less risk of inherited diseases, at least for some of the most common disorders.

While this study is far from perfect, it has ignited a new conversation about the role canine genetics plays in disease. As a veterinarian, I’ll be on the lookout for disorders in my mixed-breed patients I once reserved for pure breeds. For pure-breeds, I’ll be extra-vigilant in discussing the importance of selecting a good breeder. Hopefully this type of investigation will make us all better stewards of pet health.    



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Posted by John Outlaw
on October 06 2014 11:11

Actually, Dr. Hill, I'm surprised at your post. Most doctors understand things like "dominant" and "recessive" traits. Your question "Are humans any less prone to genetic disease due to breeding diversity? No" is completely inaccurate. Just one, very simple example comes to mind. Sickle Cell Anemia. Inter-racial children have nearly 0 risk of acquiring sickle cell anemia. And their children, if bred with another caucasian, even less of a chance to be a carrier. There are numerous genetic disorders similar to this that, if you really were a doctor, you'd know.

Posted by Dr. Mary Eleanor Hill
on September 26 2014 11:05

I have been breeding Chesapeake Bay Retriever since the 1980's and been owned by them since childhood some 65+ years. In addition, my father bred beagles along with chessies. Genetics is genetics - if both parents are carriers, the pups will be affected or carriers. It does not matter if they are the same breed. Are humans any less prone to genetic diseases due to breeding diversity? No, inheritance leads to the potential of disease, environment and other situations lead to the manifestation of the disease. I can see that in my own medical history. How do you explain dyplaysia in a dog that has certifications for 3-4 generations? Genetics, no matter how to try to prevent it the transmission of disease can happen.

Posted by Leslie Brown
on January 09 2014 10:41

interesting article to be shared with our patients' owners at my hospital.

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