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A blog by Jane Brackman, Ph.D.
jlbrac@earthlink.net

Thursday, April 19, 2012

DOG SCIENCE - CAUSES OF DEATH IN PUREBRED DOGS


This post is the first in a series I'm doing about dog science.  I'll provide links to easy to read summaries of the science. And to add a little context, I'll include links to similar studies - some with different findings.  If you want to know more you can jump in from there.


This post is about breed-related causes of death. Mortality is 100% no matter what the breed (or species for that matter), but if you want to know what will likely be the cause of death of your favorite purebred dog, then read this journal article.

Mortality in North American Dogs from 1984 to 2003: An Investigation into Age-, Size-, and Breed-Related causes of Death, by J. M. Fleming, K. E. Creevy, and D. E. L. Promislow

The science is pretty techy, but the charts and graphs are well explained.  On the other hand, if you like your science summarized in easy to read format,  then check this article out:  Breed-Specific Causes of Death in Dogs Revealed in Landmark Study

A FEW CAVEATS
I've listed some interesting statistics below, but before you read on here are a few things to remember:
  • Without exception, the highest killer of dogs in the US is euthanasia of unwanted shelter dogs.  If you've got room for one more (and who doesn't), please ADOPT!
  • Most dogs don't die of the diseases cited in these studies, rather they are euthanised to relieve suffering caused by the disease.
  • Statistics are helpful but they cannot tell the whole story.  For instance, if dogs of a certain breed are mostly killed by gastrointestinal bloat in middle age, then we don't know what the cancer rate is, because onset of cancer is usually later. 
  • More important than the general cancer rate in a breed is what kind of cancer and which organ is affected.  You can find out if you read the studies I've cited here in depth.  
  • What these studies don't tell you is average age of onset.  Some breed-specific cancers are diagnosed in dogs as young as five or six.
  • To give you cancer rate frame of reference, keep in mind that the cancer death rate in people is around 20-23%.  

LITTLE BREEDS
Little breeds are more likely to die of heart disease or metabolic disorders like pancreatitis or diabetes than cancer.  In general their cancer rates are under 10%.  For instance:
  • Chihuahua  7%
  • Dachshund  9%
  • Pekingese  8%
  • Miniature Pinscher - 4%

Little breeds die in accidents more often than big dogs:
  • Dachshund 11%
  • Pomeranian 13%
  • Pekingese 13%
But this probably just means that big dogs are more likely to survive an accident than a little one.

However, this is interesting.  The two breeds at highest risk for accidental death are the Jack Russell Terrier (19%) and the Australian Heeler (20%).  I'm guessing these are on-the-job mortalities like encounters with snakes and horses that don't end well.

MIXED BREEDS

Mixed breeds were included in the study.  They die of the same diseases, but it's more difficult to predict what those might be.  Like dogs in general, cancer is the biggest killer - 27%

BIG BREEDS
Big breeds are more likely to die from cancer and gastrointestinal diseases. Cancer rates in some large breeds:
  • Rottweiler 29%
  • Saint Bernard 27%
  • Rhodesian Ridgeback 37%
  • Vizsla 36% 
SOME SURPRISES
It's no surprise that Bulldogs die from respiratory disease, but so do Afghans and Vizslas.  This was an unexpected finding.  And researchers were surprised to find that heart disease is the most common cause of death in Fox Terriers.

SOME FRIGHTENING STATISTICS
Breeds at the highest risk for cancer:
  • Golden Retrieve 50% (some breeders say it's closer to 60%)
  • Bernese Mountain Dog 54%
  • Bouvier des Flandres 46%
  • Boxers 44% 
A COMPARATIVE STUDY
In Sweden they did a similar study using statistics from pet insurance records (most dogs in Sweden are insured).  The paper is well written and easy to read but the charts and graphs are difficult to understand. If the science is too technical jump to the end and read the discussion.

Mortality in Over 350,000 Insured Swedish dogs from 1995-2000: I. Breed-, Gender-, Age- and Cause-Specific Rates

Their cancer findings were different.
  • Bernese Mountain Dog 41%
  • Boxers 37%
  • Golden Retrievers 30%

SOME GOOD NEWS
Morris Animal Foundation is conducting a lifetime study of 3,000 Golden Retrievers that will identify genetic, nutritional and environmental risk factors for cancer and other diseases in the breed.  Read about it here:  History's Largest Dog Study Gets Ready for Takeoff    Better yet - donate!










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