How Long Will Your Dog Live?

Source: normanack photo - Creative Commons License

Dogs have a short lifetime, which to me is, perhaps, their greatest flaw.

I suppose that, over the past few months, I have been thinking about the lifespan of dogs more than usual. It has not been very long since I lost my Nova Scotia Duck Tolling Retriever, Dancer, who, in addition to being incredibly handsome, was one of the best working dogs I've ever owned. Had he lived one more week, he would have been 16 years of age.

Then, completely unexpectedly, I lost my sociable and gentle Beagle, Darby, who was barely 9 years old. So with that bias to my current thought processes, it is not surprising that my attention was caught by a new research report that appeared in the journal Preventative Veterinary Medicine¹which attempted to create a current life table to predict the life expectancy of dogs.

The research team was headed by Mai Inoue of the School of Agricultural and Life Sciences at the University of Tokyo. It was particularly interesting because it looked at a huge sample, namely 299, 555 dogs, who were insured by a Japanese pet insurance company (Anicom) over a one-year data collection span (2010 to 2011).

During that time period, 4,169 dogs died. The researchers looked at the causes of death, however that analysis was rather general since coarse classifications were used. They noted that the most common cause of death involved neoplasias, (which are tumors and cancers) and these accounted for 15 percent of the mortalities. Next in line were cardiovascular problems (9 percent), urinary system disorders (6 percent), digestive system disorders (6 percent) and neuromuscular system disorders (5%).

Of much more interest was the fact that the researchers had enough data to be able to construct a set of tables to predict the lifespan of dogs. I have taken the liberty to recast their data into a format which would be more understandable by a general reader.

The first level of analysis involves an "expectancy of life" calculation. Simply put this is a prediction of how many more years of life a dog has remaining, given his current age. Calculating this sort of thing is not as simple as it seems, since your expected remaining lifespan changes in a mathematically complex manner as you age.

For example, if the expected lifespan of a dog is 10 years of age, and he now reaches the age of 10, the fact that he is still alive and well indicates that he still has more expected years of life, even though he is exceeding the average lifespan of his kind. If we collapse the data across all breeds and sizes of dogs, at birth the expected length of life of dogs based on this data set would be 13.7 years. The year-by-year changes in life expectancy are shown in Table 1.

Table 1

Source: Based on data from Inoue et al (2015)

However, that analysis, while interesting, ignores a very important factor that helps to predict the longevity of dogs — namely their size.

It has long been known that the giant dog breeds, like Mastiffs, Irish Wolfhounds, and Newfoundlands, have a shorter life span. These researchers divided the dogs into five groups based on their average breed size: toy (less than 5 kg or 11 lb), small (5-10 kg, 11-22 lb), medium (10-20 kg, 22-44 lb), large (20-40 kg, 44-88 lb) and giant (greater than 40 kg or 88 lb).

When they analyzed the predicted life expectancy of a dog based on its size, they found that the greatest longevity was for the small dogs, with the toy and medium breed groupings lagging behind by a little bit. These three breed groups all had predicted lifespans in excess of 13 1/2 years. The data shows that the large breeds die approximately a year sooner, and the giant breeds some three years earlier as can be seen in Table 2.

Table 2

Source: Based on data from Inoue et al (2015)

If we further analyze this data, given the information based on breed size and the current age of the dog, we can create a life table. This life table works as follows: Given your dog's current age, and your dog's size, for any one year we can predict the probability that your dog will die in this current year.

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I have recast this data into the form of percentages to give you the percentage of dogs of a given age that would be expected to die in that one year time interval. As you can see from Table 3, the expectations are lowest for dogs between one in four years of age. It is not surprising to find that the first year is a wee bit dicey since puppies do have problems and some to prove to be fatal. However, after the fourth year of age the probability that the dog will pass away increases, and this increase is much steeper for the large and the giant breeds.

I was surprised at how quickly the larger breeds aged and their risk increased. For example, by age 5, the giant breeds already have a greater than 1 in 20 likelihood of dying before they are 6 (6.7 percent) which is 10 times greater than the risk of mortality in a toy breed of the same age (0.6 percent). If one of the giant breeds reaches the age of 9 they have an approximately 1 in 6 chance of dying before they are 10 (17.2 percent). This makes the risk of death in a giant breed more than five times greater than that of a toy or small breed who has also reached the age of nine years.

Table 3

Source: Based on data from Inoue et al (2015)

I suppose that it was already common knowledge that bigger dogs died younger, however, these data seemed to confirm this point in a very graphic manner. At the very least these tables can provide information to dog owners so that they can have some idea as to what the risk factors are for their dogs depending upon their age and size.

Stanley Coren is the author of many books, including The Wisdom of Dogs.

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