Why Don't Big Dog Breeds Live As Long As Small Dog Breeds?

Fido's time on earth may have a surprising determining factor.

Big dog and a small dog, differing lifespans

In the animal kingdom, it's almost always true that bigger mammals live longer lives. For instance, at anywhere from 75 to 100 tons, the gigantic bowhead whale can live for more than 200 years, while at anywhere from 0.59 in. to 27 in, the tiny chameleon lives an average of just five to ten. The humble fruit fly? It's lifespan can be as short as 40 days.

However, because things are never as clear-cut as they seem, one animal out there stands out among the rest as an outlier to the trend: the canine.

Yes, it's a scientifically-proven fact that small canines tend to live longer than the bigger breeds. In fact, according to one German study published in The American Naturalist, every 4.4 pounds of body mass on a dog reduces their life expectancy by approximately one month—and yet the question remains: Why?

"[Big dogs'] lives seem to unwind in fast motion," explained Cornelia Kraus, lead researcher of the dog longevity study and evolutionary biologist at the University of Göttingen in Germany. In other words, bigger dog breeds age at a much more accelerated pace, and because of this they are more likely to develop detrimental health issues that shorten their lifespan significantly.

Studying this saddening phenomenon, researchers from the College of Veterinary Medicine at the University of Georgia decided to analyze the causes of death for more than 74,000 dogs between 1984 and 2004. What they found was that gastrointestinal diseases, cardiovascular inflictions, musculoskeletal conditions, and neoplasia were all leading causes of death, particularly amongst larger dog breeds like Great Danes and Bernese Mountain Dogs.

Though scientists have been able to find an inverse relationship between a dog's size and their lifespan, the research is sparse, and there is still much investigation left to be done into why small dogs live longer than big dogs. At the conclusion of their study, even the researchers from the University of Georgia who studied dog deaths noted that their hypothesis was based off of "anecdotal beliefs and limited research," and that "detailed knowledge of mortality patterns would… contribute to the understanding of the genetic basis of disease."

Right now, what scientists have been able to hypothesize about why small dogs live longer than big dogs is this: Larger canines physically grow faster than their small furry friends, and this could be causing abnormal cell growth and fatal illnesses. However, these hypotheses are just that—hypotheses—and all that anyone can say for sure is that, though all dogs go to heaven, it seems as though the bigger ones are in more of a hurry to get there.

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