My grandmother, who raised some great family dogs, always said that mutts made the smartest and healthiest pets.
A new study of the medical records of more than 90,000 purebred and mixed-breed dogs suggests that there is some truth to Grandma's theories on canine health — but only to a point. When it comes to genetic disorders in dogs, a Maltese isn't always more likely to suffer than a mongrel.
Prevalence "among purebred and mixed-breed dogs depends on the specific condition," said UC Davis animal physiologist Anita Oberbauer, lead author of a report published Tuesday in the online edition of the Journal of the American Veterinary Medical Assn. (abstract available here).
Oberbauer and colleagues at UC Davis reviewed the medical records of 90,004 dogs evaluated in the university's veterinary teaching hospital between Jan. 1, 1995, and Jan. 1, 2010. Sorting through the records, they identified 27,254 dogs with at least one of 24 genetic disorders. The rest of the dogs were controls. The specific conditions the team studied — which included cancers, heart and endocrine disorders, orthopedic problems and other maladies — were selected because they could be diagnosed accurately, the researchers wrote.
When they assessed the prevalence of each of the genetic conditions in purebred versus mixed-breed dogs, they found that 13 disorders were equally common in both groups of dogs, including all of the cancers and hip dysplasia. Ten disorders, including cataracts and epilepsy, were more common in purebred animals, and one, a knee injury called cranial cruciate ligament rupture, was more likely to strike mutts.
(A non-genetic thing more likely to strike mutts, the data showed, was a car.)
Disorders that appeared equally often in purebred and in mixed-breed animals, the researchers suggested, may have resulted from mutations that arose long ago, in common, distant ancestors closely associated with dogs' early wolf progenitors. Such early mutations would be common in the dog population at large, they wrote, adding that "perhaps the same desired traits that made dogs a favorable species for domestication were linked" to the diseases that seem to appear at similar rates in all kinds of dogs.
The mutations that cause disorders more common in purebred animals, on the other hand, probably emerged more recently, from common ancestors that all dogs in a particular breed, or group of breeds, would share.
For more on the genetics of man's best friend, check out this story about how wolves evolved to become dogs, by former Times reporter Rosie Mestel.