"It has been publicly discussed for years that hereditary disorders would be a direct consequence of the strict selective breeding of pedigree dogs and that for this reason the purebreds would have a much greater risk of developing hereditary disorders than mixed breed dogs.Nevertheless, the findings of this study in the lay press and among purebred fanciers were not so clearly expressed. This study concluded that purebred dogs have a higher risk of at least 10 of the 24 genetic disorders examined. (See Methods and Materials: Statistical Analysis in Bellumori et al 2013 for details.) Therefore, in the graph below, positive values (above the horizontal line) indicate that the odds risk is greater for purebreds, and negative values indicate greater risk for mixed breeds. Asterisks (*) on bars indicate that in 50 comparisons of affected dogs with matched control sampling sets, there was a significant probability (p < 0.05 i.e., less than 5%) that pure and mixed breed dogs differed in expression of the condition. To make the data easier to visualize, I have computed (OR* = 1-OR), for which equal risk in purebred and mixed breeds dogs would have a value of 0, and higher odds for purebreds would have OR* > 0, and higher odds for mixed breeds would have OR* < 0. An equal risk for a disorder in purebred and mixed breed dogs would have an OR = 1. The data in the study are presented as a mean odds ratio (OR) comparing purebred to mixed breed dogs. (Note that they indicate subclassifications of epilepsy but counted it as a single disorder in the list of 24.) The abstract of the paper is included at the bottom of this page.ġ) The incidence of 10 genetic disorders (42%) was significantly greater in purebred dogs.Ģ) The incidence of 1 disorder (ruptured cranial cruciate ligament 4%) was greater in mixed breed dogs.ģ) For the rest of the disorders examined, they found no difference in incidence between mixed and purebred dogs. The study by Bellumori et al (2013) used medical records from the veterinary clinic at UC Davis for more than 27,000 dogs and compared the incidence of 24 genetic disorders in mixed versus purebred dogs. To get beyond the anecdotes, what we need are data, and a recent study provides them. What makes this complicated is that there are many purebred dogs that live long, happy lives, and others that do suffer from an inherited disorder, and of course the same can be said of the mutt of mixed heritage. The argument from one side is that mixed breed dogs are healthier than purebreds, and this is rebutted by purebred breeders as a fallacy. I haven't traced the history of this debate, but I imagine it has been fueled by two issues: first, the high burden of genetic disorders in purebred dogs, and second by the sentiment of some that people should adopt shelter dogs instead of purchasing a purebred. Much ink has been spilled arguing about the health of mixed breed and purebred dogs.
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