Why large dogs live fast—and die young

NEW ORLEANS, LOUISIANA—For most mammals, size matters: Large ones, such as elephants and whales, live far longer than small ones like rodents. But among dogs, that rule is reversed. Tiny Chihuahuas, for example, can live up to 15 years—8 years longer than their much larger cousins, Great Danes. Now, a team of undergraduates may be closer to figuring out why. The most likely culprit? More harmful oxygen free radicals in fast-growing, fuel-burning puppies.

When an organism grows, its cells break down food to make the molecular fuel they need. But generating this energy can also generate an unwelcome visitor: renegade molecules called oxygen free radicals. These molecules are missing electrons, and as they try to poach them from other cells in the body, they can quickly damage cell membranes and eventually contribute to cancer and other diseases. Molecules known as antioxidants neutralize these free radicals. But ultimately, the more energy a body produces, the more free radicals it makes, and consequently, the more antioxidants it needs. Some scientists think that escaped free radicals contribute to aging, although this is hotly debated.

To find out whether that might be true in canines, undergraduates Josh Winward and Alex Ionescu from Colgate University in Hamilton, New York, asked veterinarians for the ear clips, dewclaws, and cut-off tails of puppies and the ear clips from old dogs that had recently died. Altogether, they collected about 80 samples from large and small breeds. Working with Colgate animal physiologist Ana Jimenez, the students isolated cells from those tissues, grew the cells in a lab dish for a few weeks, and then analyzed them.

In the adult dog cells, energy and free radical production was about equal in the two breed sizes. But in the puppy cells, that balance was off. Adult large and small dogs had about equal amounts of antioxidants, but the cells from large breed puppies had too many excess free radicals for the antioxidants to fight, the undergrads reported here last week at the annual meeting of the Society for Integrative and Comparative Biology. That’s likely because large breed puppies have fast metabolisms, growing faster and requiring more energy than smaller breeds, Winward says. Cell damage even at this young age can have long-lasting effects.

The results are preliminary, and there are other ideas about why dogs age the way they do. But if the findings hold up, it might be possible to extend large dogs’ lives with antioxidant supplements for puppies, Winward suggests. These antioxidants could help get rid of those young dogs’ extra free radicals before they do damage.

Adam Brasher, an undergrad studying the effects of oxygen free radicals at Auburn University in Alabama is cautious. Excessive amounts of these molecules can be detrimental, he concedes, “but moderate levels are beneficial.” To figure out what level of antioxidants are helpful, and whether their findings apply more broadly to other breeds, Jimenez and her students plan to expand the current study next summer. “Stay tuned!” she says.