 |
The theory of hybrid vigor suggests that dogs of mixed ancestry will be healthier than their purebred counterparts. In some cases this might be true, because inbreeding among purebreds has made some breeds prone to various genetic health problems. Mixed-breed dogs are sometimes less likely to have certain genetic disorders, as their parents come from a more diverse genetic pool so that detrimental recessive genes are less likely to occur in both parents.
For example, large dogs such as German Shepherd Dogs often suffer from hip dysplasia. Mating a German Shepherd carrier of the faulty gene with a dog from a breed not known to suffer genetic hip problems reduces the likelihood of producing offspring with the problem. On the other hand, breeding the Shepherd with another Shepherd whose ancestors do not have the genetic problem also has this effect.
Hybrid vigor is not guaranteed in a mixed breed dog, however. Breeding a German Shepherd who carries hip dysplasia with a Golden Retriever who carries hip dysplasia will give mixed breed puppies who carry or have hip dysplasia.
Since most genetic defects are common to many different breeds, it is impossible to guarantee that a breeding of any two dogs will not result in defects unless you know the health history of those two dogs' ancestors and/or have had genetic testing on the dogs. Because of this, the most common genetic problems are nearly as common in the mixed breed population as they are in the purebred population.
Some purebred dog breeds have difficulties associated simply with the exaggerated physical traits of the breed. For example, the French Bulldog has such small hips and such a large head that artificial insemination and Caesarean section are usually required to produce puppies. Crossing such a dog with another breed will likely produce dogs without these reproductive difficulties, although most authorities on dog populations discourage reproduction among crossbreeds and mixed breeds because there are already so many purebreds available for adoption in addition to mixed breeds.
There is no guarantee of good genetic health of any dog, purebred or otherwise, as not all damaging genes are recessive. Also, of course, purebred and mixed-breed dogs are equally susceptible to nongenetic ailments, such as rabies, distemper, injury, and infestation by parasites. |
|