In this article, Dr. Goldston describes in general terms the aging process, changes in body tissues, special needs of the senior pet and just what constitutes a senior pet.

This is the first of a series of monthly articles I will be writing for This specific article will probably be the most difficult to understand and probably the most boring. However, it is necessary for you to know what I define as a "Senior Pet" and "Aging". It is also covers what happens to the tissues and organs of the body during aging as well as normal things that can influence the aging process.

First, how I define “Senior” and “Age/Aging” is different than the 7-7 rule commonly used.  The 7-7 rule that has been generally accepted by the public, veterinary industry and also much of the veterinary profession proclaims that dogs and cats begin their senior years at 7 years of age and that one year of the life of a dog or cat is equal to 7 years of human life. 

For the majority of dogs and cats, this is reasonably true.  However, when longevity (life expectancy) is factored into the weight of the pet and in some cases the breed of the pet; then the 7-7 rule fails demonstrably.  A study in 1988, published in 1989 (Goldston) and updated in 1992 (Goldston), more appropriately shows the relationship of the age of a “senior pet” when the pet’s adult weight is factored into the equation (Table 1). 

The part of the 7-7 rule that implies dog and cat age in relation to human age is roughly 7 years of human age for one year of dog/cat age.  However, over one-half century ago, the original study of dog years to human years revealed that the first year of a dog’s age equated to 12 years of human age.  The second year of a dog’s age equated to 24 years of human age and thereafter each one year of a dog’s age equated to four years of human age (LeBeau, 1953).  Amazingly, without factoring in the breed or the breed size, this remains remarkably true today.



Small dogs                       0-20 lb:           10 years
Medium dogs                 21-50 lb:              9 years
Large dogs                  51 -110 lb:              7 years
Giant dogs                       >110 lb:              5 years
Cats (domestic)                                        10 years

I am sure this study will be refined more in the future when the American Kennel Club determines the average longevity of each breed.  Of the breeds studied to date: Saint Bernard’s (Saint Bernard Club of America), Irish Wolfhounds (Bernardi, 1988); each have a total life expectancy of 6.5 years and the Burmese Mountain dog 6.2 years (Goldston, 2000).  Using the 7-7 rule, they would already be dead before they became “seniors”!  Of the small breeds studied the Maltese, Miniature Schnauzer, Miniature Pinscher, Pomerian and Shih Tzu had an average life expectancy of 13 years (Goldston 2000).  This corresponds very closely to reviews by the AKC for several of breeds American Kennel Club 2002).  The AKC reported the Chihuahua as having the longest life expectancy that being 15 years (American Kennel Club 2002). Using the 7-7 rule, these breeds would just barely be over middle age.

In another study of longevity over a 10-year period for six giant breeds of dogs and seven small breeds of dogs, there was significant evidence that the small breed dogs lived longer than the giant breed dogs. Only 13% of the giant breed dogs lived to be 10 years of age or older, and only 0.1% lived to be 15 years of age or older.  On the other hand 38% of the small breed dogs lived to be 10 years of age or older and 7% lived to be 15 years of age or older (Deeb and Wolf, 1994).

As I have previously mentioned there are several variables that influence when a pet dog or cat is considered to a senior pet.  These I have classified in Table 2 and will discuss individually.



Genetics - Small breeds of dogs live longer than large breeds. Mixed breeds out live pure breeds.

Nutrition - Obese pets live shorter life spans than non-obese pets. High fat and/or low fiber diets decrease life expectancy.     

Environment - "Outdoor" animals have a shorter life expectancy than "indoor" animals. Rural animals out live urban animals. Spayed females, but intact males live longer.*    

There is no doubt that genetics determine the adult size of the pet and has considerable influence on the pet’s longevity and when the pet reaches “senior” status. Studies of all sub-primate animals show that cross or mixed breeding increases longevity and vitality. This is referenced in agriculture as “hybrid vigor.”

In all mammals, individuals whose weight exceeds 20% of desired weight have a decreased life expectancy. Outdoor animals in an urban environment have a decreased life expectancy due to an increase in exposure to disease causing agents plus an increase in death by trauma.  Conversely rural animals have a decreased chance of disease exposure and trauma.

Statistics show a definite and significant increase in life expectancy of female dogs and cats that have been spayed relative to those left intact. Statistics also show a tremendous increase in longevity in male cats that are neutered relative to those that are intact e.g. not neutered.

* However, statistics show a slight increase in longevity of dogs that are not neutered vs. those neutered.

HOWEVER, I strongly advise that all male dogs that are not going to be used for breeding be neutered.  Furthermore male dogs that are going to be used for breeding should be neutered once they are no longer going to be used in breeding. I will explain this in detail in a later article.


The percentage of the body weight represented by fat increases and muscle weight decreases. This means the six-year-old forty-pound dog has much more muscle and less fat than the same forty-pound dog at twelve years.

Skin becomes thinner and loses its elasticity. The skin around the rectum and scrotum becomes thickened and pigmented in non-neutered males.

Footpads thicken and form calluses, the nails become brittle and more care is needed to maintain the pets comfort level.  Nutraceuticals, proper bedding and in many cases protective coverings as specialty shoes are required.

Muscle, bone, and cartilage tissue decreases, causing progressive joint disease, weakness and the development of arthritis occurs.  Nutraceuticals as Omega 3-7 fatty acids and other anti-inflammatory medications are needed.

Dental calculus results in tooth loss.  Veterinary dental care, oral disinfectants, natural dental cleansing agents, etc. are needed.

Dental disease from infection (Periodontitis) causes loss of gum tissue and tooth root exposure, causing tooth loss occurs.  Again gum disease must be treated with veterinary care, Nutraceuticals, oral disinfectants and cleansers are needed.

The stomach lining mucosa becomes thinner and less functional.  Digestive aids, probiotics, enzymes, etc. are needed.

Liver cell numbers decrease and liver cirrhosis occurs. Diets higher in marine fats, plant fats, more biodigestible protein (eggs, etc) may be needed.

Formation of digestive enzymes from the pancreas decreases, resulting in decreased digestibility of fats, carbohydrates and proteins. Nutraceuticals and digestive enzymes are needed.

Lungs lose their elasticity and lung secretions become thicker and harder to expel.  This is further complicated by a reduction in the cough reflex and forcefulness. Subsequently COPD (Chronic Obstructive Pulmonary Disease) increases with age.

Urinary incontinence frequently develops resulting in urine leakage, especially when sleeping. Special bedding and special diapers may be needed.


I have tried to describe in general terms the aging process, changes in body tissues, special needs of the senior pet and just what constitutes a senior pet in this article.  Future articles will deal with more specifics on aging problems, disorders and diseases.  Also, I will go into as much detail as possible as to what you as a senior pet owner can do to make your senior pet’s years truly the “Golden Years”.

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  • Updated: 4/25/2018: 11:02:29 AM ET
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