I read a comment elsewhere yesterday that it's a myth that mixed breed dogs are generally (on average) healthier and longer-lived than purebreds.

I thought, in general, with a bunch of disclaimers, but in general, that it was pretty much accepted that the median age of death of companion (pet) dogs was a later age for mixed breed than for purebred dogs.

In fact, I read somewhere about a big (20,000 animals, or maybe more) study in this country that there was almost a two-year average difference in life span. Weight classes were compared, but then the aggregate average was that almost-two-year difference.

The "myth" comment was followed by comments about mixed breeds not being screened, and mixed breeds being no less vulnerable to many problems, including some genetic ailments. But no numbers and no backup were supplied.

I'm curious about this now. This isn't something I've ever really looked into.

I'm also wondering if anyone else remembers the study I remember, based on data from North American vet reports about average lifespans.

Part of the reason is that so many purebreds are line-bred. The study referenced below found that it doesn't take much to knock a few years from a dog's expected lifespan.

The pursuit of specific appearances by very close breeding also tends to concentrate health defects. And, those 'valuable' dogs are bred in spite of those defects. That is how bone cancer became embedded so deeply in Golden Retrievers. A popular and overused stud had that weakness. No, that line is deeply embedded in the breed.

I can't put my finger on it just now but it was somewhere on this site.
http://users.pullman.com/lostriver/breeddata.htm

(added)
Bingo! Nothing on the internet is ever lost.
http://www.netpets.org/dogs/healthspa/longevity.html

Note his comments about how quickly line-breeding affects longevity.

Lot's of other cross-species stuff is out there on how in-
breeding/line-breeding affects fertility.


Edited by Charlie Snyder (04/17/2012 02:45 PM)
Edit reason: found reference

why nobody ever bred FOR longevity is a mystery to me, Wolves live up to twenty years in captivity which busts the myth that large dogs don't live as long as small dogs. Bitches I recently learn will ovulate their entire lives which tells me that dogs aren't living to their maximum penitential age.

Line-breeding will definitely concentrate good qualities in a particular breed however it also concentrates the undesirable traits. Breeding out the undesirable traits is a long term process and may never be achieved. Line-breeding and breeding to the flavor of the month has all but ruined Chihuahuas. It was difficult to get a well balance, sound puppy years ago, today it's nearly impossible. We need to stop breeding to feed our egos and start looking at the lifespan and quality of life of the puppies we produce. I doubt it will ever happen with the breed I was involved in but it's about time breeders started having honest conversations about problems within their line and stop hiding them in the kennel.

That sounds preachy as I re-read this, don't want to offend anyone but I have strong feelings on this topic.

There is "bad breeding" in both mutts and purebreds but mutts have the advantage that often the bad breeding that results in them does sort of come down to natural selection. A yard (or community) full of loose dogs breeding freely and the less healthy ones aren't going to be the ones being bred. In intentionally (but still irresponsibly) bred mutts (designer dogs) you see TONS of horrific genetic problems that aren't affecting the puppy from the hoarders yard where over the years dogs are bought in, fights break out, food is scarce, the weaker ones die off, the survivors breed.

Purebreds, EVERYONE breeds purebreds but very few to it right. Lack of testing, breeding things that require help to breed due to physical problems, overlooking things that would result in death if the dog got out for even a day and you end up with some lousy purebred stock. Even good breeders may overlook a disorder if the rest of the dog is solid just because it gets harder and harder to find a dog with a trait they like. It's not just dogs either, color breeders in horses....there's a reason so many Cremello horses are hideous in conformation, their aren't as many of them so people think "oh, well he's got the breed color even with those nasty pasterns", it's worth it. In working dog terms, getting a certain specimen of a breed with a temperment enough to do work is getting harder, therefore a stud with some genetic condition (maybe he's a carrier) that previously wouldn't haven't been considered because of that condition that works well may be bred, puting his offspring at risk and their offspring.

Personally I think that more breeds should have open stud books and outcross regularly to keep the health of the breed. Any dog with no more than 2 "other" breed in 3 generations of it's pedigree should be considered purebred. Breeding in an outcross to a pointer got rid of the uric acid issues in Dalmatians. Dutch shepherds tend to be healthier than some of the other shepherding breeds. Dogs used for hunting are often mixed between various crossbreeding breeding programs and they're pretty solid to, same with a lot of herding dogs. They cull ruthlessly and outcross frequently when they find something they like but it makes for a healthier dog (and for the record, my support of culling means that the culls shouldn't breed, not that they should be destroyed). Plus there is a definate "type" to those dogs. They may not be as identical as two AKC registered purebreds from a show line but if you look at two healthy sound dogs of competely different breeds there is a lot of similarity in their conformation.

I don't know about life span, but I do know that the derma vet said she sees almost as many mixed breeds as pure breeds when it comes to allergies!!

I've seen inbred and line-bred mixed-breeds. Too many of them, actually. The difference is that it's an accident of opportunity and the results are very arbitrary.

I have also seen some very serious structural issues in mixed breeds: Bad knees, hips and elbows, eye problems, etc. just like with purebreds. My mother has a mixed-breed dog that had two knee surgeries before she was four years old, and is likely to need surgery on at least one hip.

Beyond the physical health stuff, I have also seen a lot of temperamental/stability issues in mixed breeds.

I'm not a fan of line-breeding. It's pretty tough to find a purebred dog that hasn't been line-bred (or inbred)at some point in it's history, but my personal preference has been to stay as far from it as possible. Otherwise, I like my purebreds. I like knowing that a dog's parents and grandparent etc. have been screened for health problems and I like to have some idea (within reason, of course) what the temperament and tendencies of my animal are likely to be.

I can't really speak one way or the other to longevity in pure vs. mixed, but I do know that my Dobe and my Mom's dog are the same age, and my large dog is aging much more slowly than her medium dog. When they were both puppies I assumed it might be the other way around.

There may be too many factors in play to draw an accurate conclusion about mixed vs. pure.

Some breeds do live longer than others. Toy fox terriers, schipperke (? sp) I've seen at 18, 19.
On old dog is great, it would be wonderful if they all lived to 20.

Years back it was more common for folks to put money in keeping a purbred dog "healthy". That or those were the folks that had the money to even buy a purebred. The mutts made it or they didn't because of possible economic issues. Spay/neuter wasn't as common and more dogs were left to roam. The survivors/strong were the breeders.
Today's furbaby generation is more apt to put money in whatever they own so "IF" it ever was true I don't think it's the case now.

I have to agree with Kristel, just because they are mixed breeds choosing who they mate with doesnt mean that they are getting culled by survival of the fittest. Most of the mixed breeds who Ive witnessed having puppies were bred (or let breed) by people who owned the dogs and there was even less purpose in the breeding than there is with designer dogs or purebreds. And yes, there seems to be a lot of line breeding in those situations for some reason...
They may have more robust genetics just because they were crossed out of the breed at some point but a lot of times ignorant people (and I unfortunately know several) are breeding mothers to sons and so on for no apparent reason except that they thought their dogs enjoyed it.