A rare scientific study on animal health explains for the first time why larger dogs have a shorter life expectancy than smaller dogs: Selective breeding for size has made large breeds more susceptible to cancer.
This is one of the most outstanding results of a study led by experts from the University of Adelaide (Australia) in which they have examined the causes of differences in life expectancy and death in 164 breeds of dogs, ranging from Chihuahuas to Great Danes.
The results of this research have been published in The American Naturalist magazine. "When we looked at these data sets, we found that larger dogs were more likely to die from cancer at a younger age compared to smaller dogs," said Jack da Silva, a researcher in the University of California's School of Biological Sciences. University of Adelaide and co-author of the study with Bethany Cross.
"Larger dogs did not necessarily age faster than smaller breeds, but research showed that as breed average body weight increased, cancer rates also increased," the authors write in a news brief released by your university.
"We think the relationship between a dog's body size and lifespan may be due to an evolutionary lag in the body's anti-cancer defenses, which cannot keep up with the recent rapid selective breeding of larger dogs. "Jack da Silva proposes.
The study found that the shorter life expectancy was consistent with a theory of aging known as life history optimization or "disposable soma."
"This theory is based on the idea that if you invest most of your resources and energy in growth and reproduction, you cannot also invest them in cell repair and defenses against cancer. In all organisms, attention is focuses on early reproduction, even if it comes at the expense of maintaining and repairing the body and living longer," Da Silva explains.
The results could also be useful when looking at aging in humans.
"Dogs represent a good model for studying aging in humans. Dogs, like humans in the industrialized world, live in an environment that tends to protect them from accidental and infectious causes of death and are therefore more likely to die from age-related diseases, such as cancer", details the first author signing the study.
Although the results of this survey may be worrisome for large dog owners, researchers predict that larger breeds will evolve to develop better cancer-fighting genes.
"Most of the 400 or so dog breeds we know of today only became established in the last 200 years. Larger dogs haven't had time to develop better cancer defense mechanisms to match their size. This still It could happen, but it can come at a cost for reproduction," says the researcher.
Jack da Silva predicts, on the other hand, that larger breeds will adapt and extend their lifespans, but according to the aging theory, they are more likely to have smaller litters in the future.
"This can occur naturally or through selective breeding, as people focus on breeding larger dogs that have lower cancer rates and therefore greater longevity," Da Silva explains, according to his university. .
Da Silva and Cross are now investigating the connection between litter size, cancer rates, and life expectancy in dogs and other mammals.
