There’s a common belief that mutts are healthier than purebred dogs but this belief is not backed up by data. Veterinarians in the United States do not normally keep or report health data on dogs by breed or cross but there has been extensive investigation in Europe. Health problems with purebred dogs are easier to detect and report because their breeds are identifiable. Breed clubs and dog health registries keep track of their health problems so they can work to improve the health of the breeds. No one records health data for mutts so their health problems usually go unreported. This doesn’t mean they are healthier or that they don’t have health problems.
What is hybrid vigor?
Some people claim that mutts must be healthier because of “hybrid vigor.” That is, the parents of a dog are completely unrelated so they can’t share any harmful genes in common and therefore the dog must be healthier than a purebred dog which is, by definition, more closely bred. Hybrid vigor does indeed exist but genetic diseases in dogs are widespread. Just because a dog might have a Labrador and a Poodle for parents doesn’t mean he will be free of genetic diseases, for instance. Labradors and Poodles share some genetic diseases such as Progressive Retinal Atrophy (PRA) and hip dysplasia (which is considered to be partly genetic in some cases). The same is true for many other diseases found in dogs, regardless of the breeds involved. In addition, some diseases are dominant so even if a dog has two completely unrelated parents of different breeds, one of the parents could have a gene for a disease that is dominant and which would appear in the puppies. Genetics is a complex subject and mixed breed dogs are subject to canine diseases just as much as purebred dogs are.
There are estimated to be somewhere between 400 and 500 genetic diseases found in dogs. That probably seems like a lot until you consider that there are thousands of genetic diseases found in humans.
Purebred dogs and their Health Issues
Purebred dogs certainly do have health issues, just as all dogs can. If you look up information for each breed you will find that there are usually several genetic diseases that can appear in a breed. This is because each breed represents a subset of the larger canine population. Just as German Shepherds don’t have all of the genes found in all dogs, they don’t have all of the genes for all canine diseases. But they have genes for certain diseases that can afflict them. Obviously, breeders try to avoid breeding dogs with health problems. Today there are many advanced ways to screen and test dogs to weed out dogs that carry genes for particular diseases so breeders don’t breed them. But we don’t have a test for every single potential health problem. Sometimes unexpected problems occur. Sometimes the law of averages is unpredictable. For example, a breeder could have several generations of puppies without any health problems and then, suddenly, a serious problem crops up. A recessive gene could have been hiding for generations waiting to meet another recessive gene when the breeder made a certain mating. It’s impossible to avoid every problem forever.
Repeated inbreeding will bring all genes in a dog’s pedigree closer together, both desirable genes and undesirable genes. If there are hidden recessives which might bring out disease then repeated inbreeding will bring out the disease in dogs, too. Most breeders avoid very close inbreeding, however. The Kennel Club in Britain estimated recently that only about 1 percent of all dogs registered were the result of father-daughter, mother-son, or sibling matings. They have since banned inbreeding this close. The practice is also rare in the United States and Canada.
Compared to mutts, purebred dogs are very closely bred. Many breeders practice what is called “linebreeding” which is breeding a dog to a relatively distant relative. However breeders are more mindful today about the importance of avoiding genetic diseases.
Health registries such as the Orthopedic Foundation for Animals http://www.offa.org/ record the results of health testing on dogs. Different breeds use different tests, depending on the problems found in each breed. The registries record the information so other breeders and potential puppy buyers can look up information about particular dogs. This is a great tool for breeders when planning matings so they can choose dogs with good health clearances.
Owners of mixed breed dogs could have their dogs tested for any of these diseases and report them to OFA or other health registries but few if any do so.
In terms of lifespan, most large scale surveys have found that mixed breed dogs and purebreds live about the same length of time when they are cared for by loving owners and have regular vet care. Small and medium-sized purebred dogs such as Whippets, Miniature Poodles, and Jack Russell Terriers had the longest lifespans with some living to be 17 years old or more. Giant purebred dogs such as Irish Wolfhounds had the shortest lifespans because of heart problems. Old age for an Irish Wolfhound could be 9 years. Medium-sized mixed breed dogs usually live moderately long lives when they are well cared for by loving owners.