Why Do Small Dogs Live Longer Than Large Dogs?

On average, tiny dogs live almost twice as long as really big ones -- and science isn't entirely sure why. Learn what we know (and don't know) in this episode of BrainStuff, based on this article: https://animals.howstuffworks.com/pets/longest-living-dog-breeds-tiny.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff, a production of iHeart Radio. Hey,
brain Stuff, learn vogal bomb here. Have you ever wondered
why you seem to know a lot more elderly Chihuahuas
than aged Rottweilers. It's just a fact of life that
small dogs, if they escape disease or misadventure, live longer

(00:22):
lives than larger ones. This trend has puzzled veterinary researchers
for as long as we've been fussing over our faithful
four legged friends, and it's a mystery that hasn't been
definitively solved. Conventional wisdom in the animal world dictates that
between different species, larger animals live longer than smaller ones.

(00:43):
For example, an elephant can live into its seventies, while
a mouse might only have a year or two to
do its earthly business. However, the opposite seems to be
true within single species subsets, and although dogs come in
lots of shapes and sizes, they're all the same species.
The average lifespan for an enormous dog is around seven

(01:04):
or eight years, while a tiny dog can reliably live
to the ripe old age of fourteen or fifteen. The
popular adage that one human year is equal to seven
dog years isn't supported by modern science. Although it's easy
math and therefore sticks around. The truth is more complex.
In the first year of a dog's life, it generally

(01:26):
reaches the physical maturity of a fifteen year old human.
The second year adds another nine years, and after that
the rate of aging varies widely based on breed and size.
A small dog is considered senior at around age eight,
while a large dog hits old age around five or six.
Researchers know this, but they're not entirely sure why, and

(01:48):
to be fair, it probably involves a combination of a
lot of different factors. It turns out that a dog's
size isn't the only, or even the primary factor that
determines lifespan. Genetics and breeding also play a role, with
certain breeds being more vulnerable to certain life threatening or
life shortening diseases and conditions than others. Basically, although the

(02:11):
aging process for dogs is very different than it is
for humans, it's also very different. Among dogs. The features
that a dog has been bred for seemed to matter
more than size. There was a study published in April
two in the journal Nature based on a massive database
of veterinary records from the United Kingdom, and to keep

(02:32):
it simple, they looked at the lifespans of pure bred dogs.
Small jack Russell Terriers, and midsized Border collies differ substantially
in size, but according to the study, they live pretty
similar lifespans twelve point seven and twelve point one year's respectively. However,
flat faced breeds like pugs and French bulldogs were found

(02:52):
to have much lower life expectancies due to breathing problems,
a disease, and difficulty giving birth. The French bull dogs
life expectancy is only four point five years, and none
of the other flat faced breeds, no matter how small,
were found to have an average lifespan of more than
seven point eight years. Okay, but why might size matter.

(03:16):
It might have to do with how long it takes
a dog to become full grown and the difference in
size between its puppy body and its adult body. It
seems that growing very large, very quickly takes time off
of a dog's overall life span. Take, for example, a
Great Dane. In the first two years of their life,
they reach their full size, which can be over thirty

(03:39):
or eighty centimeters tall, and some a hundred and seventy
five pounds around eighty kilos. That's a lot, and it
apparently takes a toll. Large breeds die of cancer more
often than small breeds, a trend that researchers believe has
to do with how quickly they grow in their first
year of life. With all that rapid expansion, it possible

(04:00):
that abnormal cell growth is more likely, or because their
lives play up more quickly, that they succumb to the
diseases of old age earlier than say a chihuahua. It
takes a chihuahua about ten to twelve months to grow
to full size, but that size usually maxes out at
only about eight inches or fifteen centimeters tall and six pounds,
which is just under three kilos. It's just not as

(04:23):
taxing on the body to become a full grown chihuahua
as it is to become a complete great dane. Finally,
lifestyle and access to veterinary care can affect longevity, and
these factors can depend on the role of the dog
within the family. For example, toy dogs may be pampered
more than larger breeds given their lap friendly size. And

(04:47):
all of this isn't just important in terms of figuring
out how we might all spend more time with our
beloved companions a dog. Research is also important because dogs
die of the same illnesses that humans do, including answer
heart disease and diabetes, and so as usual, learning more
about them may help us learn more about ourselves. Today's

(05:12):
episode is based on the article the longest living dog
breeds are tiny, but Why on how stuff works dot Com,
written by Jesslyn Shields. Brainstuff this production of I Heart
Radio in partnership with how stuff works dot Com, and
it's produced by Tyler Clang. For more podcasts, my heart
Radio is the I heart Radio app, Apple Podcasts, or
wherever you listen to your favorite shows.