Large dogs generally live shorter lives than small ones. A new study could help explain why.
A Great Dane lives on average for less time than a Chihuahua. This is surprising because, in the animal kingdom, larger species often live longer than smaller ones. Researchers therefore looked for what distinguishes large dogs from others as they age.
A Great Dane, a large dog breed. Photo: Dühring Fotografie, via Wikimedia Commons.
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They analyzed the blood of 894 dogs. They focused on small chemical marks found on DNA. These marks change with age and can be used to estimate the aging of cells without altering the DNA itself.
The researchers thus obtained a kind of “biological clock.” And surprisingly, in large dogs, this clock seems to advance more quickly. In other words, two dogs of the same age can show different signs of aging. Those whose clocks were the most advanced also had a higher risk of death.
To explain this difference, the researchers examined certain DNA fragments nicknamed “jumping genes.” They have this name because some can copy themselves or change position within DNA. Normally, chemical marks help keep them inactive.
However, in large dogs, these marks disappear more with age. The “jumping genes” could then become active and disrupt cells. This is a possibility, not yet a certainty: the study did not show that they actually became more active.
The researchers also observed changes in the cells that defend the body against disease. They do not yet know whether these changes contribute to shortening the lives of large dogs.
The next step will be to follow the same animals for several years. This will show whether the changes in DNA actually accelerate aging or are simply a consequence of it.