Dog aging is affected by its genetics, size and weight. Body frame and size directly relates to rate of aging. Smaller breeds of dog, in general, age at a slower rate than medium and large breed dogs. Giant breeds (i.e. Great Danes, Irish Wolfhound) have a shortened life span as a rule. Extra body weight, regardless of body frame or size, will also accelerate the aging process. In addition, the burden of extra weight can cause medical problems that are normally associated with old age to occur in young or middle aged dogs.
Body Fat Affects on Aging Process
The amount of fat in the body can also affect the aging process. Overweight pets can accumulate fat around the abdominal organs causing subtle changes in the functioning. The extra pounds create further stress on the cardiovascular system and the liver. Extra weight also means more work for the joints and muscles. This can accelerate the aging process and lead to arthritis and back problems. In addition, as the animal ages the metabolism slows decreasing muscle mass and increasing fat accumulation.
Why Small Breeds Age More Slowly
In general, larger and heavier dogs have a reduced life span compared to smaller lighter dogs due to the effects on the body of large size and heavy weight. They have more osteoarthritis problems and more strain on internal organs due to larger size. However, not all small breeds are long lived. Some breeds of small and medium sized dogs are more prone to their own set of particular health problems which reduce their life span. In addition, the environment a dog is kept in influences their life span. Outdoor housing of a large dog with inadequate shelter will expose a dog to illness and other animals which may injure a dog. It is easier for an outdoor dog to be neglected as well.
Approximating Age in "Dog Years"
At the age of 5 a dog less than 20 pounds is the human equivalent of 36 years. A dog over 90 pounds at the age of 5 is the human equivalent of 42 years. At the age of 10 a small dog is approximately 56 human years. A large dog at the age of 10 is the human equivalent of 78 years. The average life span of a small dog is 14-15 years. Large breed dogs are long lived if they reach the age of 12.
With proper nutrition, exercise and medical care all dogs will have a better quality of life and live to their full potential.