Dogs, like people, are unique. From appearance and behaviour to genetic disease susceptibility and lifespan, dogs on both a breed and individual level are very different to one another.
A recent publication by McMillan et al. investigated this latter difference, more specifically the “Longevity of Companion Dog Breeds”. But what did they find out? And did it agree with what we previously thought? Let’s find out.
Table of contents
First, a genetics concept or two
“Survival of the fittest” is a concept made famous by no other than Charles Darwin himself. Put simply, it is the idea that only organisms most adapted to their environment will be able to survive. For example, camels are adapted to survive in the harshest of deserts, being able to walk for days to find food and water via their ability to conserve body fat and minimise water loss. Such advantageous traits can be passed down to their offspring, making them in turn more likely to survive their environment as well.
“Genetic variation” is a similar concept, as it refers to the variability in genetics between individuals. More specifically, it is the difference in genes between organisms. And these genes can be to do with anything, for example fur density, skin colour, muscle coverage and limb length. With this genetic variation, comes the ability to be more or less suited to an environment. For example, increased fur density allows better survival in cold environments, as is the case with the Husky breed.
So, it is generally accepted that in most situations, the more genetically variable a species is, the more likely it can survive its environment.
Purebred dogs
Back to dogs, and the topic of this article. Are purebred (/ pedigree) dogs more affected by genetic disease? Put simply, the answer is yes.
Through breeding dogs with “desirable” physical characteristics, such as flat faces or curly tails, we have inadvertently selected for disease-causing genes. Think of it as we bought one desirable gene and got one undesirable gene free. For example, through breeding so called “Pedigree” flat faced dogs (such as Frenchies, Pugs, Bulldogs) we have caused these breeds to have extreme breathing difficulties. Another, less obvious, example is the breeding of Cavalier King Charles Spaniels. Through breeding these dogs to look exactly how we want, we have inadvertently bred in mitral valve heart disease (this extra genetic coding is sometimes known as a “spandrel”).
Crossbreed dogs
Crossbreeds are a mixture of at least two different dog breeds. Their parents are either different breeds to one another, or crossbreeds themselves. Therefore, their offspring are a genetic cocktail of breed information. This often makes them more resilient to genetic disease through something called Heterosis.
Heterosis, or hybrid vigour, is the phenomenon that offspring of genetically diverse individuals, such as dogs of mixed breeds, exhibit greater genetic robustness. Thus, these dogs show greater genetic variation and furthermore are more likely to be “fitter” when considering survival.
Purebred vs. Crossbreed dogs
So, if Pedigree dogs have a higher incidence of genetic disease does this mean crossbreed dogs live longer? Not necessarily, according to the 2024 paper “Longevity of Companion Dog Breeds”. Previously it was thought that crossbreeds have a longer life expectancy, due to some of the reasons discussed above. However, this paper, with a sample size of over half a million, disputes this.
They found out that crossbreed and pedigree dogs have very similar life expectancies, with pedigree breeds actually living a little longer (12.7 years compared to 12 years). Furthermore, they found that 47.1% of purebred dogs lived longer than crossbreeds, with only 25.8% living fewer years that crossbred dogs (27.1% of the sample did not vary significantly in lifespan). There were limitations during this study, such as not considering the breed composition of the crossbreed dogs when comparing with their pedigree counterparts, but their findings are enough to make further research in this area needed before conclusions on this topic can be made.
Conclusion
In conclusion, purebred dogs have a higher incidence of genetic problems compared to crossbreeds. This is known to be true. Regarding the mentioned paper, I am not overly convinced by their findings, due to the main limitation discussed above. In order to fairly and reliably compare the lifespans of crossbreeds and purebreds, you need to compare like for like – for example, compare the lifespan of a Labradoodle with a Labrador and Poodle. However, it was a very extensive study, with a very large sample size, so their findings should definitely be considered and furthered. I am still very much in the “crossbreeds are healthier than purebreeds” camp, however I will have an open mind when reading similar studies in the future.
Discussion