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Best in Health: Purebred or Mixed-Breed?

With their extremes of limb and coat, purebred dogs may seem more prone to health problems. And don’t breeders even compound defects, as they tinker with uniformity? Yet the dog of many varieties, a potluck of traits, outlasts them all.

Not quite, say U.C. Davis researchers in a recent study lead by Anita Oberbauer in Canine Genetics and Epidemiology. Their analysis of health records of 88,635 dogs, both purebred and mixed breeds, tilts assumptions. So does another recent study, in which they found both populations shared similar risk for 13 inherited disorders. One condition was even more prevalent in mixed-breeds.

Purebreds, and their health records, have made it easier to explore the genetics of diseases that get passed down, the researchers say. But as we hear about the studies, the belief that purebreds are less healthy grows. In fact, many breeds have proven more prone to some diseases, like Great Danes and hip dysplasia.

In this study, they sliced the data thinner. Could particular AKC breed groups, not just individual breeds, be the source? Do the diseases arise from dogs with genomic similarities like working and herding groups? The huge pack of canines, seen over 15 years at U.C. Davis veterinary teaching hospital, showed that ten inherited conditions are more common in purebred dogs. But surprise, not all purebred dogs.

A subset of pedigreed pups tied with mixed breeds for the disorders.

The conditions include aortic stenosis (narrowing above the aortic heart valve or of the valve); skin allergies; bloat; early onset cataracts (clouding of the lens inside the eye); dilated cardiomyopathy (enlargement of the heart chambers); elbow dysplasia (abnormal tissue growth that harms the joint); epilepsy (brain seizures); hypothyroidism (underproduction of thyroid hormones); intervertebral disk disease (affects the disks of the spine, causing neurological problems); and hepatic portosystemic shunt (abnormal blood circulation around the liver, rather than into it).

With a spotlight on the ten maladies, the researchers set out to learn which canines are more at risk. Purebreds were subdivided into categories, then compared to the mixed breeds.

For three conditions common across the purebreds—skin allergy, hypothyroidism, and intervertebral disk disease—many groups had higher prevalence than the mixes. But for seven others, most purebred groups were statistically neck and neck with mixed-breeds. (Aortic stenosis, gastric dilation volvulus, early onset cataracts, dilated cardiomyopathy, elbow dysplasia, epilepsy, and portosystemic shunt).

Terrier groups even bested the mixes for one problem, having less intervertebral disk disease.

Among the purebred groups, health differences were clear. Compared to mixed breeds, terriers and toys were more likely to have two disorders. Herding and hound groups were more burdened with four conditions. The non-sporting group, where pooches ranging from Poodles to Dalmatians fit in, were more likely to have five disorders. Working breeds, animals expected to have grit and vigor; six. Worst in health: the sporting group bred for outdoor stamina. They were more at risk for seven inherited disorders.

In fact, in three categories of dogs bred for endurance—herding, sporting, and working AKC groups—aortic stenosis, the heart condition present at birth, was higher. With narrower focus, other findings emerged. The researchers say the data “suggests that most breeds in the herding group are not at higher risk”—except the German Shepherd, which other studies have also found susceptible.

And while Retrievers were more affected by aortic stenosis, another sporting breed, the Spaniel, wasn’t. For a different malady, Spaniels were the unluckiest. Epilepsy was more prevalent in herding, hound, and sporting groups, particularly the Spaniel breeds.

Early onset cataracts beset both non-sporting and sporting breeds more often.

How did all of these health glitches arise? The study mentions other research that found some diseases, like elbow dysplasia, are more frequent in dogs of related ancestral origin. The so-called “liability genes” may hail from founding ancestors of related breeds, or be the result of human error in the quest for desired traits. This study, the authors say, “may shed light on the possible origin of certain inherited disorders in domestic dog evolution.”

For the ten diseases, the analysis found some purebreds genetically healthier than others. Flipped around, mixed breeds were no healthier than certain purebreds. But both populations may benefit from the work. According to the researchers, defining the lineage associations for such disorders may bring about new therapies.

Better, it could allow breeders to weed out the responsible genes to begin with. Especially at the local level. “Whether breeding reforms will mitigate inherited disorders in mixed-breeds will depend upon the locale,” the scientists say. That is, some regions have a greater potluck of breeds within their mixed-breeds.

Still, since most mixes have purebred ancestors, they say, improvement of the genetic health of purebreds “may trickle down to mixed-breed dogs.”

 

 

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Sheila Pell is a journalist and contributor to The Bark.

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