Whenever I’m asked by a potential new dog owner which breed I would recommend for their family, the mutt appears somewhere on the list. We’ll go over a series of questions to determine what size, energy level, and personality traits best suit their family dynamics and then come up with a few possibilities for breeds that might be good matches.

 

I put strong emphasis on the fact that individual variation can always trump breed predilection. For example, Labrador Retrievers have a well-deserved reputation of being good family dogs, but I’ve met a few that I wouldn’t let anywhere near a child.

 

Along the same lines, I always mention that mutts can be the most charming and healthiest dogs out there. I tend to see my mixed breed patients only for preventive care and the occasional accidental injury until the infirmities of old age catch up with them. Conventional wisdom states that when dogs with dissimilar genetic makeups mate, their offspring have a lower chance of developing diseases that require the inheritance of two recessive alleles. This is the genetic basis of hybrid vigor.

 

A recent study published in the Journal of the American Veterinary Medical Association confirms that mixed breed dogs suffer from fewer genetically based diseases, but the details reveal some interesting subtleties that are important. The researchers reviewed the medical records of over 90,000 purebred and mixed breed dogs looking for a diagnosis of any of 24 genetic disorders. Statistical analysis revealed the following.

 

Ten disorders were more prevalent in purebred dogs:

 

  • aortic stenosis
  • dilated cardiomyopathy
  • hypothyroidism
  • elbow dysplasia
  • intervertebral disc disease
  • atopy (allergic dermatitis)
  • bloat
  • cataracts
  • epilepsy
  • portosystemic shunt

 

Cranial cruciate ligament rupture and being hit by a car (which says more about owners than the dogs themselves) were the only conditions more likely to be observed in mixed-breed dogs than purebred dogs

 

No differences in the frequency of diagnosis of the following 13 genetic disorders were detected.

 

  • all the cancers that were evaluated (hemangiosarcoma, lymphoma, mast cell tumor, and osteosarcoma)
  • hypertrophic cardiomyopathy
  • mitral valve dysplasia
  • patent ductus arteriosus
  • ventricular septal defect
  • hip dysplasia
  • patellar luxation
  • hypoadrenocorticism (Addison’s disease)
  • hyperadrenocorticism (Cushing’s disease)
  • lens luxation

 

Frankly, I was surprised by the number of genetic diseases that affected purebreds and mixed breeds equally. The paper’s authors postulate that genes for these traits may “have arisen multiple times or the progenitors of the affected dogs may have been derived from a common distant ancestor carrying the defect. Mutations introduced into the dog genome earl y, in an ancestor closely associated with the wolf progenitor, would be spread through the dog population at large.”

 

Other explanations are also possible. For example, selection for non-breed specific traits (e.g., size) might play a role, different genetic mutations could have similar effects, and/or a dog’s environment might overwhelm its genetic predisposition. As the authors point out, “No significant difference was found for cancers between purebred and mixed-breed dogs. Genes for cancer expression may be spread widely among the dog population as a whole, respond to environmental factors that affect all dogs, or a combination of both.”

 

 

Dr. Jennifer Coates

 

 

Source

Prevalence of inherited disorders among mixed-breed and purebred dogs: 27,254 cases (1995-2010). Bellumori TP, Famula TR, Bannasch DL, Belanger JM, Oberbauer AM. J Am Vet Med Assoc. 2013 Jun 1;242(11):1549-55.

 

 

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