As a general rule of thumb, a dog who is 7 years or older should be considered middle to senior aged. According to the UC Davis Book of Dogs, small-breed dogs (such as small terriers) then become geriatric at about 11 years; medium-breed dogs (such as larger spaniels) at 10 years; large-breed dogs (such as German Shepherd Dogs) at 8 years; and giant-breed dogs (such as Great Danes) at 7 years. As with humans, advanced years often bring changes in a dog's ability to hear, see and move about easily. Skin condition, appetite and energy levels often degrade with geriatric age, and medical conditions such as cancer, stroke, renal failure, incontinence, arthritis and joint conditions, and other signs of old age may appear.

What is the relation between dog years and human years? It is not linear!

Three types of calculations are used but...

• Popular myth — it is popularly believed that "1 dog year equals 7 human years" or the like. This is inaccurate on two scores, since the first year or two years represent some 18–25 years, and the ratio varies with size and breed.
• One size fits all — another commonly used system suggests that the first two years equal 10.5 years each, with subsequent years equaling four human years. This is more accurate but still fails to allow for size/breed, which is a significant factor.
• Size/breed specific calculators — those try to factor in the size or breed as well. These are the most accurate types. They typically either work by expected adult weight or by categorizing the dog as "small", "medium", or "large".

Approximate graph of dog years and human years (defined as how much each species ages in a year), allowing for differing sizes of dog.

No one formula for dog-to-human age conversion is scientifically agreed on, although within fairly close limits they show great similarities. As a rough approximation, the human equivalent of a one-year-old dog is between about 10 and 15 years—a one-year-old dog has generally reached its full growth and is sexually mature, although it might still be lanky and need to fill in a more mature musculature, similar to human teenagers. The second year is equivalent to about another 3 to 8 years in terms of physical and mental maturity, and each year thereafter is equivalent to only about 10 or 11 human years.

Life expectancy by breed

Factors affecting life expectancy

Apart from breed, several factors influence life expectancy:

• Diet - The oldest dog on record was Bluey, an Australian Cattle Dog, who died at 29 in 1939. In the 2000s, at least two dogs were still living at 27 years old, but one was fed a purely vegetarian diet (border collie, died at 27) and one fed primarily on kangaroo and emu meat (bull terrier cross, died at 27).
• Spaying and neutering - Neutering reduces or eliminates the risk of some causes of early death, for example pyometra in females, and testicular cancer in males, as well as indirect causes of early death such as accident and euthanasia (intact dogs roam and tend to be more aggressive), but there might increase the risk of death from other conditions (neutering in cited paper only showed an increased risk for prostate cancer but has not been repeated in subsequent papers] in males, and neutered males might have a higher rate for urinary tract cancers such as transitional cell carcinoma and prostatic adenocarcinoma.

DVM, Dr Wim Van Kerkhoven
Viyo International
Website : www.viyo-elite.com