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How Old is an Old Dog?

By Dr. Bob Encinosa


Everyone has heard the old saying that each year in a dog’s life equals 7. Well as much as I appreciate simplicity, this generations old ratio of life expectancy is simply not true. Unfortunately there is no formula that works for all breeds and sizes of dogs.
In the animal kingdom as a whole, there is a general rule that applies in most cases. The larger the animal, the longer it lives. Elephants live longer than mice. Grouper live longer than minnows. Giant tortoises live longer than terrapins. However, within a single species the opposite is usually true. Small people live longer than large people (on average), and small breeds of dogs live longer than large breeds. Chihuahuas and poodles commonly live to 15 years or more, while Irish Wolfhounds rarely live beyond 8 years. Other breeds, such as Boxers and King Charles Cavalier Spaniels also have shorter life expectancies due to specific breed related diseases.


So how do we arrive at a comparative age in human terms for our dogs? Let’s take an average 40 pound dog for an example. At the age of one year, this dog would be nearly full grown and capable of reproduction, the equivalent of a teenager, perhaps 13 or 14 in human years. During the next 10 or 11 years, each year of the dog’s life would equal about 4 human years, so that at the age of 12, this dog would be nearing 60 in human terms. After that, the rate increase again to about 7 to 1, making this 15 year old dog the same relative age as an 80 year old human.
Giant breeds may take over 2 years to reach full size and sexual maturity. However, they tend to have a relatively short middle-age and greatly accelerated senior years.
Another general rule is that mixed breed dogs, aka mutts, tend to outlive purebred dogs, on average. This is due to a phenomenon known to geneticists as “hybrid vigor”. This crossbreeding tends to dilute some of the undesirable genes that are the source of many diseases.


So how can we extend the life of our dogs? The genes that God gave them cannot be changed, so we’re left with environmental factors. Assuming that you’re already taking care of the easy stuff, like proper veterinary care and immunizations, heartworm prevention and keeping them safely confined, you’re left with just a couple of things. Just as in humans, two of the biggest factors are diet and exercise. With regards to diet, there is little to no evidence to show that the type of food a dog eats will extend its life. So long as the food is a complete and balanced diet, the quantity of food consumed is by far the biggest factor. The less a dog eats and the leaner it stays, the better. Whether the food is organic, raw, gluten free, all meat or vegetarian does not matter nearly as much as ensuring that you do not overfeed your dog. Apparently this rule of controlled intake applies to most if not all species, including cats, horses and humans. So…..smaller portions please!