This study was performed in April 2005 using a telephone surveys. It is an interesting study.
Now, one should be careful generalizing form such narrow set of cases. After all, those provinces in Italy could have some sort of environmental conditions that affect the development of tumors in these animals.
Before I put too much weight into such studies, I would like to see similar studies performed in other parts of the world. If the results are similar, then we can say that pure-bred dogs are at a greater risk for spontaneous tumors.
We do know that the genetic diversity of many purebred dogs and cats is lower than the genetic diversity in their mixed counterparts, simply because they are bred in a closed registry system that has just a few founders within that registry. This problem is further exacerbated with strong line-breeding, in-breeding, and the most-used sire effect. More inbred animals are known to have weakened immune systems.
That means that purebred animals are more likely to have compromised immune systems and, thus, might make them more susceptible to cancer. That’s the theory about why so many inbred strains of vertebrate species are susceptible to cancer.
That’s why we should think about opening up registries.
***
Now I am going to have to muddy the waters a bit.
I’m citing it because it seems to contradict this line of reasoning, and as someone who tries to be fair on this blog, I think it is worthwhile to point out some interesting contradictions that sometimes appear in the scientific literature.
Now, don’t get me wrong. I’m for open registries for all sorts of reasons (mainly because most other studies contradicts this study.)
Anyway, I just posted this to engage in some dialogue.
[…] A study suggests that purebred dogs and cats have more cancer than random-bred ones « Retrieverman'… retrieverman.wordpress.com/2009/10/19/a-study-suggests-that-purebred-dogs-and-cats-have-more-cancer-than-random-bred-ones – view page – cached A study suggests that purebred dogs and cats have more cancer than random-bred ones — From the page […]
In the Study you point out that shows inbreeding as a positive…. sort of falls flat on its face since its based on human populations, the most important factor removed from that example is ironically the “human factor”. Now if the study were to focus on breeding of humans for type, where there is a conformation standard driving the decision of the pairings….. then I believe it would render this entire study as irrelevant and moot.
Canines in the Dog Fancy are paired mostly by human decisions to preserve a specific look or quality that is desired. Not driven by the lust and desires of the individual dog. In fact if the dogs show no interest in each other….. the “Human Factor” will make it so any way. If more randomness were introduced, and now culling or surgical culling were practiced…. the results would possibly be very different.
Fads and standards are the root of it. The Registries only exacerbate the final result. Ultimately it is the consortium of breeders that sealed the fate of their breeds. With the exception of only a few specific breeds…. all of them have been taken to their current status by Humans.
I posted it, not because I thought it was generalizable to all vertebrates but because it was an apparent contradiction of what most of us say about inbreeding.
I agree with you, though.
That MHC link is fantastic. Great explanation. I am going to steal it.
True story: an acquaintance of mine with Salukis, imports from the Middle East, bred a litter from what were thought to be unrelated dogs. almost all the pups ended up with some kind of auto-immune disease. They checked the MHC on the parents (there is a lab in Finland that does this), and it was identical on both parents. anectdotal but interesting.
MHC studies are the same kind my sister (also a Geneticist) agrees with. And one of the reasons I take everything with a grain of salt from most breeders outside my circle of sister Kennels.