You probably haven’t heard of Agnes Sligh Cambell. She was born in America in 1888, the daughter of two Scottish immigrants. She liked to write and published several novellettes that have mostly been forgotten. But you may have read an extract of hers, which circulates the Internet in meme form today:
“Dogs’ Lives are too Short. It’s their only fault, really.” Agnes Sligh Turnbull
This certainly resonates with me: even Bluey, the record-holding Australian Cattle Dog, didn’t make it into a third decade (7th June 1910 – 14th November 1939) and humans can easily live four times that long. For me, the saddest part of a vets’ job is not the act of putting an animal to sleep (it is often the right thing to do) but witnessing the end of an incredible bond and the intense suffering of the owner.
So how long can a dog be expected to live?
The answer, of course, is ‘it depends’.
There are sometimes said to be seven dogs years in every human year. This is an approximation; there is little science in it. Furthermore, human lives vary dramatically in length and so do dogs.
There is much more difference generally between families of dogs than families of people
Sure, people come in different colours and different builds, with different facial profiles and capabilities. Some ethnic groups are associated with longevity, although it is hard to separate genetic factors from environmental factors – is it good genetics or good diet in some cultures, for example?
The genetic variation between nations of people is nothing to the variation between different breeds of dogs, who have been deliberately bred in separate lines for hundreds and hundreds of years. Thus dogs can be as different as
All have the same number of chromosomes though: they are all still part of the one species, just like us.
Dogs with the same shaped bodies tend to suffer from similar diseases to one another.
So it is probably not surprising that a dogs’ lifespan seems to depend on its breed:
In general, the larger the breed, the shorter the expected lifespan. According to a recent report in New Scientist, Chihuahuas, for example, can be expected to live for around sixteen years; an Irish wolf-hound typically for five.
This is odd, because for most mammals, the pattern is in the opposite direction.
Mice live for around one year, blue whales for seventy to ninety. The reason for dogs having the opposite trend is not clear. Scientists suggest that the smaller the dog, the faster the metabolism and the faster ‘free radicals’ are cleared from the body. ‘Free radicals’ is a delightful name for products of metabolism that damage body cells and DNA.
Can we cheat the system and help dogs to live longer?
It is already well known that dogs with an appropriate diet and level of exercise live for longer. But can we manipulate free radicals to make a big difference? A recent article in New Scientist suggests that the answer may turn out to be ‘yes.’
There is a drug called Rapamycin, which is generally used to suppress immunity, that has recently been found to have an effect on the lifespan of dogs!
This works by altering the way that free radicals damage the body. The drug has already been shown to make a significant difference to mice, with one mouse in the trial living for over three years.
Wow! So you’re saying that I can give tablets to extend my dogs’ lifespan?
Theoretically, it may well be possible: early findings have been very encouraging. There were reports a few weeks ago that a small group of dogs were given the drug for over ten weeks, and while this isn’t long enough to pick up any significant changes in lifespan, it did turn out to be long enough to observe subjective improvements in liveliness and well-being, and have positive effects on the function of the animals’ hearts. This study has now been extended and The Dog Aging project, in Washington, Seattle, are recruiting dogs for a longer, more significant, trial.
This sounds like the Elixir of Life from Harry Potter!
It’s obviously excellent news for the individuals concerned and certainly brings us one step closer to having our best friend by our sides for much longer.
However, the ethics of extending life-span like this – not to mention the fact that the cost and supply may well be in the hands of private companies – is likely to come under some scrutiny. Side effects of the drug have not yet been identified. Once such a drug is workable in animals, extending its use to the human race seems to be the next logical step, but also the stuff of science fiction.
Meanwhile, I would suggest that paying attention to a dog’s weight, diet and exercise levels (and being mindful of inherited joint and heart issues) are probably the best way for now of supporting longevity in our best friends.