Are mixed breed dogs inherently more healthy than purebred dogs? Do mixed breed dogs suffer from genetic (inherited) diseases at the same rate that purebreds do? This is a question that was recently addressed by Dr. Mary Fuller in a post entitled Mixed Mutts and Designer Crosses: Healthier than Purebred Pets? Her conclusion is no, mixed breeds, particularly the so-called “designer breeds”, may not necessarily be healthier or less likely to inherit genetic conditions than a purebred dog.
In fact, Dr. Fuller mentions a study that looked at this question more closely.
“In a five-year study of veterinary cases at the University of California-Davis, there was no difference between mixed-breed and purebred dogs in the prevalence of common inherited disorders. Even designer-bred dogs were being seen with hereditary conditions that it was assumed crossbreeding would eliminate: hip dysplasia, epilepsy, cancer, hypothyroidism, eye disorders and more.”
I do believe there is some credibility to the theory of “hybrid vigor”. However, there are mixed breeds and then there are mixed breeds. My grandmother used to refer to many of the mixed breed dogs around their neighborhood as “Heinz 57 dogs”, meaning that they had genetic makeup from many different and totally unrelated sources. Though these dogs can still have genetic disorders, that’s still a far cry from the “designer breeds” where both dogs (dam and sire), though of different breeds, are often still very highly crossbred or inbred within their breeds, concentrating the genetic makeup of those lines in their pedigrees. Obviously, the entire concept is much more complicated but, as Dr. Fuller says in her post, “If you cross a Labrador Retriever that has hip dysplasia with a Poodle that has hip dysplasia, what do you get? Chances are, a Labradoodle with hip dysplasia.”
That brings me to my next point. If you’re breeding a pet of any species responsibly (whether dog, cat, horse or other type of animal), you should be doing all you can to remove undesirable genetic traits from the gene pool. That means that you probably shouldn’t be breeding one dog with hip dysplasia to another dog with hip dysplasia anyway. This is true whether you’re breeding purebreds or “designer dogs”. Breeding for improvement means choosing animals that are good examples of the breed they represent both phenotypically (the way they look) and genotypically (their genetic makeup). It also means planning a mating between compatible animals with traits that complement or improve on each other.
Unfortunately, what is happening with “designer breeds” is not much different than what is happening with purebreds. There are too few responsible breeders and too many “backyard” breeders who see these animals as a means of making money. Worse yet, puppy mills have jumped on the “designer breed” bandwagon as well. These breeders are breeding animals that are not the best representatives of their breeds and, as a result, creating puppies (and kittens) that are genetically flawed as well. I take my hat off to responsible breeders but not so much to the others.
As Dr. Fuller (correctly) asserts in her post:
“Before breeding, all animals be tested for heritable conditions such as hip dysplasia, deafness and eye disorders, as determined by....READ MORE