A recent blog post by Dr. Stanley Coren mused about “hybrid vigor” or the notion that mixed-breed dogs are healthier — or, at least, less prone to genetic diseases — than purebred dogs. I decided to read the full study he referenced to learn more.
A large group of researchers, mostly Finnish, studied a huge sample of dogs: more than 83,000 mixed-breed and more than 18,000 purebred dogs of 330 different breeds. They analyzed the dogs’ genotypes, looking for 152 different genetic markers that underlie hereditary diseases.
They quickly narrowed down the study: Of the dogs with a faulty gene, 96 percent had one (or more) of a group of 30 genetic markers or “disease alleles.” They narrowed further, selecting the nine most common markers, which all appeared in multiple purebred breeds as well as in mixed-breed dogs in the sample.
Several findings might be interesting to dog owners:
- Mixed-breed dogs are as likely or more likely to carry some genetic variations linked to diseases than purebred dogs.
- But purebred dogs are more than twice as likely to actually have a genetic disease.
That makes sense; the number of purebred dogs who are actually bred is quite small, and many are bred to dogs from the “same lines” — relatives, even very close relatives. Within a closely related population, the likelihood of dogs sharing a recessive gene is much higher than in the broad population of mixed-breed dogs. - Deeper study of individual mixed-breed dogs who carried rare genetic variations found that, even when the dogs exhibited symptoms of a genetic disease, these individual dogs were only diagnosed after the owners had the results of the genotyping.
That also (sadly) makes sense: The vets didn’t suspect that the mixed-breed dogs had rare, usually breed-linked, genetic diseases.
The question of “hybrid vigor” is nuanced, since the dogs are likely to be carriers but less likely to suffer the diseases, but I’d argue that mixed-breeds are healthier.
In his post, Coren also points out that another common belief — that breeders frequently breed dogs known to be carriers or even sufferers of a disease — is unfounded. Many breed-specific genetic diseases have become extremely rare or have been eradicated — due to careful breeding. Some breed clubs forbid breeding of carriers of known genetic diseases.
The researchers are sharing their data; they’ve created the free My Breed Data database, where anyone can search for information on genetically linked diseases.
The Thinking Dog 
Though agree with most of the article the statement of breeders do not inbreed or breed dogs that have genetic issues — that is plan hogwash. I do not know of a single responsible breeder. I know they are out there but here in Texas there are none. I have had numerous arguments with breeders and every time they were proven wrong.
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Most mixed breed dogs are not hybrids though, so hybrid vigour doesn’t apply to them although they are of course much more genetically diverse than pure breeds (unless they are inbred… mixed breeds can be inbred too, usually by accident).
Hybrids means offspring of parents from genetically separate populations (“genetic silos”). For example, a F1 cross bred dog such as a true labradoodle is a hybrid, but a multigenerational “labradoodle” (a labradoor/poodle blend but not F1) is not.
Here is a good example of how hybrid vigour is used in pig production in Denmark (and probably in the industry more generally): Four breeds of pigs were/are used in pig production: two “sow breeds”, Landrace and Yorkshire, and two “boar breeds”, Duroc and whatever the last one was; these are bred by the pure breeders. The purpose of industrial pig pure breeding is to be able to produce ideal crosses in the production link, aiming to optimise hybrid vigour for many different aspects hereunder growth, health, litter sizes and piglet survival and many other relevant aspects.
The pure breeders work hard to optimise their lines of course (for specific aspects in each specific breed), but the pure breeds invariable perform poorer than the cross breeds, which is to be expected, and therefore the pure bred industrial pigs are expensive – because the breeders need to be compensated for their lower output compared to the production animals.
Then, (other?) breeders breed the gilts, that are to become the production sows; these are normally F1 crosses between Yorkshire and Landrace (hence why they are called the sow breeds), so they are hybrids. The production sows are then bred to one of the boar races, so that the production pigs (the ones we eat) are crosses between at least 3 pig breeds. All that because hybrid vigour is a major factor that has significant impact on productivity & profitability, and in pig production it isn’t about reducing the risk of genetic diseases but general vitality such as growth, health, fertility and many other aspects.
So I’m laughing when some people say that it is a “myth” that designer (F1) crosses are healthier. Of course their health and quality depends on the quality of the breeding stock and how they are raised and all that sorts of essential things that matters for all dogs, but if *everything else is equal* then yes they’ll benefit from hybrid vigour, and it is a real significant thing that affects general vitality – a multitude of aspects, not just genetic diseases… although of course in hybrids the risk of two recessive genes meeting each other is minimised, so that too.
PS. I used to work in pig production in Denmark. It is many years ago, but a quick google suggests that the system hasn’t changed in regard to the above aspects
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(“the risk of two recessive genes meeting each other is minimised”… what I mean is of course that: the risk of the same recessive gene meeting its copy in an offspring, is minimised… I hope that was clear)
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Pam Hogle, thank you for your blog post.Really thank you! Awesome.
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