In the animal kingdom, a larger body typically means a longer lifespan. We see that across species and orders. For example, a large lizard like the Komodo dragon can live up to five decades. Meanwhile, a much smaller reptile, like an anole, only lives for about five years. That's true across the animal kingdom. Bigger animals simply live longer. However, there's one exception: Dogs.
In the canine world, smaller dogs live much longer lives than their bigger counterparts.
A great example is a Great Dane and a Chihuahua. Chihuahuas can live 12 to 18 years, if not longer. Sadly, Great Danes rarely make it to 10 years old. Most only live six to eight years.
So, what gives? Why are canines the exception to the rule? Scientists believe that they've discovered why big dogs die young.
Faster Aging
One study found that the answer to this puzzle lies in how quickly large dogs age. Mark Elgar, an evolutionary biologist at the University of Melbourne, says that large dogs age significantly faster than their smaller counterparts. Thus, there is more strain on the physiological processes of bigger breeds, which causes faster mortality.
Elgar turns to a North American study analyzing death data from 74 breeds. This study highlights the tradeoff between size and lifespan. It finds that bigger dogs age more rapidly, resulting in more physical and biological "wear and tear."
Many people turn to the "seven-year rule" to understand their pup's age relative to human years. However, dogs don't age the same way as humans, and they don't age the same way as every other breed. Some age faster than others, and size is a big factor in that equation.
Bigger dogs require far more energy to fuel their body. The biological processes from birth to adulthood take their toll quickly in large-breed canines.
Escaped Free Radicals
Another study points to free radicals in the body as a reason why bigger dogs age faster and die younger. Free radicals are unstable molecules with unpaired electrons. When the body grows, it breaks down food to create the molecular fuel it needs. However, the breakdown process can also generate oxygen free radicals.
The problem with free radicals is that they try to take electrons from other cells to compensate for the electrons they lack. As they try to poach electrons, the free radicals damage cell membranes. This process can lead to the development of cancer and other diseases.
Because large breeds have bigger bodies, they need more fuel. Thus, they break down more food to create fuel, which results in the presence of more damaging free radicals.
A study at Colgate University in Hamilton, New York, found that large-breed puppies have far more free radicals in their bodies than even adult dogs.
In addition to free radicals, the body also produces antioxidants to neutralize them. However, the experiments conducted during this study found that large-breed pups had too many free radicals for the antioxidants to fight.
The findings showed that free radicals greatly damage a young dog's body. While the amount of these damaging free radicals decreases as the dog ages, the damage done during puppyhood has lasting effects that could cause bigger breeds to die sooner.
Riskier Living
Another potential factor to consider is how large dogs live versus smaller ones. While every breed has a unique personality and penchant for physical activity, larger dogs tend to be more daring.
For instance, Great Danes are highly active dogs that spend their youth getting as much exercise as possible. Meanwhile, a small breed like a Shih Tzu spends most of its day lounging around.
The lifestyle of a dog matters. The more active and risky a dog is when it's young, the greater the chance it will die in an accident or develop debilitating conditions that could negatively impact its lifespan. This theory is particularly worrying for large working dogs.
Enjoy the Time You Have
Researchers continue to learn more about aging and mortality in dogs of all sizes and breeds. Some theorize that strategies like providing antioxidant supplements can help lengthen the lifespan of bigger pups. However, there's no concrete evidence to prove if that's beneficial.
Life expectancy for domesticated dogs has improved tremendously in the last several decades. As dog owners invest more in providing a healthy diet and more frequent vet visits, pups live longer than ever.
If you have a large dog, the best thing you can do is enjoy your time together. Instead of focusing on the limited lifespan, apply your energy towards helping your dog live the happiest and healthiest life possible.
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