In nature large animals tend to have longer lifespans than small ones. Elephants, for example, can live as long as 70 years while mice are doing pretty well if they make it to 4. In domestic dogs the situation is reversed: large breeds tend to have shorter lifespans than small breeds. The average lifespan of a Great Dane is 6 to 8 years. Schipperkes (little black dogs) average 13 to 15 years but living into their 20s isn’t that unusual and there have been cases of Schips living as long as 28 years. Why?
Big dogs apparently die younger mainly because they age quickly, researchers say.
These new findings could help unravel the biological links between growth and mortality, the scientists added.
To shed light on the possible tradeoffs of large size, researchers analyzed ages at death in 74 breeds, using data from more than 56,000 dogs that visited veterinary teaching hospitals. The researchers focused on why large dogs lived shorter lives on average.
“My main scientific interest is life-history evolution. I’m also a bit of a dog nerd in private life,” said researcher Cornelia Kraus, an evolutionary biologist at the University of Göttingen in Germany.
The scientists found that large breeds apparently aged at faster rates; the speed at which the risk of death increased with age was greater with larger breeds than smaller ones. Indeed, among dog breeds, an increase of 4.4 pounds (2 kg) in body mass leads to a loss of approximately 1 month of life expectancy.
The implication is that the same factors that cause them to grow rapidly cause them to die early. I wonder how true that is.
In Great Danes the primary causes of death are bloat (gastric volvulus)—22.8%, cardiovascular problems—13.5%, and cancer—12.3%. Generalized “old age” is below 10%—9.9%.
Bloat is a puzzling condition (I’ve had two dogs die of it). No one really knows what causes it. I suspect it’s structural in nature. It’s known, for example, that large, broadchested breeds are more predisposed to bloat than others. I think that many cardiovascular problems are structural, too. The system just isn’t strong enough to handle the load that’s being placed on it.
Everything dies of something but it seems to me that if you eliminate the major causes of death that the odds of living a longer life will increase.
Next month our Tally will turn 15. She’s the longest-lived Samoyed we’ve ever had and has lived longer than her father, her mother, her littermate, her brothers and sisters, her grandparents, even her nephews and nieces. I think it’s because she was structurally sound, we’ve kept her weight down, she’s had great healthcare, and we’ve treated every health condition that she encountered promptly and prudently. I think she escaped the bloat that took her mother largely because of good luck—I attribute it to abdominal surgery she had earlier in life.