New tricks to keep old dogs on the prowl

We've had to make the difficult decision to say goodbye to one of our best friends.

Not a human friend, but one of the four-legged variety. Which has meant explaining to our six-year-old why dogs (and other animals) just don't live as long as people.

You might have heard the old saying that one dog year is equivalent to seven human years. Our old dog was almost 16, which would make him almost 112 in people years. That's a pretty good innings for a dog.

So what determines how long our finned, furry or feathered friends live?

In the animal world there's a general rule that the larger the animal, the longer the lifespan. A mouse might live for a couple of years. A horse might make it to the grand age of 30.

And an African elephant may outlive a person, with some living for over 70 years.

Our dogs tend to live somewhere between 10-13 years, although the oldest recorded dog more than doubled that, living for a massive 29 years.

For a long time scientists tried to explain lifespan by differences in metabolic rates - which control energy use, and capacity for growth and reproduction. Smaller animals tend to have to have higher metabolic rates - they live fast and die young.

But this isn't true for all animals. The naked mole rat, for example, is about the size of a large rat, but has been found to live up to 30 years. Even dogs themselves buck this trend - with smaller breeds tending to live longer than larger breeds.

Other researchers have been looking at aging animals and think that a long lifespan comes down to the ability to make specific proteins. In particular, proteins that can protect DNA, or repair molecular damage.

These proteins help animals to better cope with the biological changes associated with aging.

They say you can't teach an old dog new tricks. But some scientists think we might be able to trick nature, and stop our dogs aging so quickly.

The Aging Dog project is a US based research program investigating dog aging and using different pharmaceuticals to increase their lifespan.

And it's not just about giving us longer with our four-legged friends. It's hoped the project will also identify factors that influence human aging - and help us live longer, healthier lives too.

Dr Mary McMillan is a lecturer at the School of Science and Technology, University of New England