The Lifespan Of Pets Is So Short7 min read

 In General



One of the sad thoughts about pet ownership is how fast a puppy can turn into an old dog or cat. This all seems to happen in the blink of an eye.  Life passes fast for most of us but even faster for a dog or cat.  The aging process is accelerated in our companion animals.  This process is even worse for the giant breeds of dogs.  The lifespan of pets varies with the size of the dog.  The general rule of thumb is that the bigger the dog, the shorter the life expectancy. A Great Dane rarely lives to be 8 yet a tiny Chihuahua can easily live to 14-16 years of age.  Cats are more or less the same size.  The average indoor cat lives often to a ripe old age of 15 or 16 years of age.  The oldest cat I ever worked on was 23 years of age.  So, what are the many factors that are involved in the aging of a dog or cat?  Read on.




Compared to humans the lifespan of pets is extremely short. Even the beginning of life is shorter.  The gestation period for a dog or cat is about 60 days compared to 9 months for a human pregnancy.  In this short period the fertilized egg goes from basic cell division to a fully formed puppy or kitten in only 60 days.  This even includes the development of a fetal skeleton.

The young animal is born yet these early weeks pass so rapidly.  Their eyes and ears are open at 14 days of age and their body temperature becomes independent of environmental temperature. They nurse and grow larger.  At six weeks it is all over.  The young puppy or kitten is fully weaned.  Out it goes to the world at large.  Hopefully the animal finds a new home.  Compare this rapid development to that of a baby!

Dogs and cats are born without teeth.  They have their own dental eruption pattern to follow.  At 16 weeks of age they will have a full set of adult incisor teeth.  At 6 months of age they will have adult upper and lower canine teeth.  At 8 months of age the adult molars are present and it is over.  Imagine that, a complete set of teeth at only 8 months of age. A young child of 6 years barely has an upper incisor poking through the gums.

When it comes to toilet training, dogs have babies beat hands down.  Some parents start to wonder if their children will be wearing diapers when they head off to college!  Many of the hunting dogs will be completely toilet trained at 12-14 weeks of age.  Some breeds such as toy breeds are picky about the procedure but in short order something clicks and they make that special sound that means they have to go outside to void.  Yorkshire Terriers are another subject.  They are basically impossible to toilet train and the majority of owners resort to pee pads that are kept indoors.  Regardless, puppies are quite easy.

Cats have dogs and babies beat when it comes to toilet behavior.  Kittens will find their litter box even before their eyes open at 14 days of age. They are that smart!  Unless there is a physical or emotional issue regarding litter box use, the cat is a clean animal with impeccable litter box behavior.  All of this behavior occurs over a very short period of time.




The lives of dogs and cats make huge strides forward after getting out of puppy or kitten development.  The lifespan of pets is further sped up by the onset of sexual maturity.  Both dogs and cats are fully capable of reproducing between 6-7 months of age.  Big dogs mature a bit later than smaller dogs.  As mentioned earlier, pregnancy only lasts 60 days in both species.  A female is fully capable of delivering a litter way before her first birthday!
When a dog or cat turns one year of age they are considered adults!  A one year old adult animal compared to a one year old baby!  When you look at this angle you will notice the huge disparity between the lifespan of pets when compared to an average human.




The prime life period for any dog or cat is between one year of age up to about 7 years. Those are the golden years for most house pets.  In day to day medical practice the only time you would see a young animal would be for vaccinations, neutering, accidents or an allergic reaction to an insect bite.  Very basic medical care.  Most of the animals that are brought into animal hospitals for medical workups are about 8 years of age and up. This is close to the time when dogs and cats are considered senior citizens.  At an age of 8 a child is just starting the first few years of school!  His life is all ahead of him.

It is because of the short lifespan of pets that blood work often has to be repeated every year.  So much change can happen to an animal in just a one year period compared to humans.  This rapid aging process means that blood work drawn a year ago is antiquated and must be repeated. Most healthy people do not see rapid changes in their annual blood work.

Arthritis is seen in most older dogs.  Cats often don’t develop hip issues until they are about 12-14 years of age.  To look at a dog’s life at 8 or 9 years of age, we stare at it in disbelief.  Wasn’t it just yesterday that we brought that little puppy home?  That is the cruel reality of owning a pet.  The realization that someday we have to say good bye to a friend that is only now a small cuddly puppy or kitten.

I wish I had the answers for this genetic, cellular disparity between the short lifespan of pets compared to that of humans.  Maybe by studying animal cellular biology we may make a leap forward exploring why the lifespan of pets is so short.

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