Doggone myths: are mixed breeds healthier than purebreds?
PetSmart From the book “The American Pit Bull Terrier” Copyright 2006 by T.F.H Publications
Does hybrid vigor, the notion that dogs which are less related have increased fertility and health, really exist? Sure. It just doesn’t occur quite as often as people think because it is more than a matter of not mating the same breed. People assume that as long as the female and stud are different breeds, the offspring will be healthy, but that’s not necessarily true or false. Despite popular claims of hybrid vigor in all mixed breeds, it does not occur in all dogs of this type just because they are mixed breeds. According to Dr. Freshman, hybrid vigor occurs among dogs which have the least amount of genetic background in common; they generally have increased fertility and better health than those with a common heritage.
However, because you don’t know the background of the mixed breed, you cannot know for sure what genetic background the dog may share. And if each of two mixed-breed parents is predisposed to the same health problems, a mixed-breed dog can have those problems, too. In short, don’t assume that because your dog is not purebred that he is going to be wonderfully healthy and never need to see the vet except for annual exams.