Why Is There So Much Cancer In Our Dogs?


Can Early Neutering Be A Major Cause of Cancer In Dogs?

I know in advance, this writing will be controversial.  For as long as I can remember our recommendations on neutering pets has been to do this at or before the age of six months. Some say “before the first heat cycle in females”.  There is no doubt that many positive benefits result from neutering pets in both the male and female.  But I am very concerned about what emerging data is showing and the alarming rate of cancer and other orthopedic problems we are now seeing in our senior pets.

When it comes to deciding at what age a dog or cat should be sterilized, without much scientific data for proof, the standard has been sooner rather than later. This is especially true in the case of shelter animals because they often don’t see them after adoption, or can’t rely on the adopting family to bring them back to a veterinarian for this procedure.

But every practicing veterinarian has witnessed an alarming rise in cancer, and other disease, and this has caused some animal health care experts to dive into decades of available data. One question that comes up frequently is whether early sterilization is a good idea for every pet.  Several well-known cancer experts and epidemiologists have begun to ask questions about this “standard” recommendation.

A summary study almost ten years old has largely been ignored by the veterinary profession.  More than 50 peer-reviewed papers were examined Larry S. Katz, PhD Associate Professor and Chair Animal Sciences at Rutgers University to assess the health impacts of spay / neuter in dogs. The reader of this study simply cannot ignore the findings of increased risk of our pets developing life-threatening cancers such as; osteosarcoma, hemangioscarcoma, and other very common diseases such as: hypothyroidism, ligament tears and hip dysplasia.

It’s troubling to learn a procedure we’ve historically viewed as life-saving and of value to the pet community as a whole, has likely played a role in harming the health of some of the very animals we set out to protect.

What does the data say? 

One of the most common types of cancers is the hemangiosarcoma (HAS).  Spayed females had a greater than five times risk vs. their intact counterparts.  Bone cancer, the type that took my dogs life, was also shown to be significantly increased in pets neutered “early”.  Studies done in the 1990’s concluded dogs spayed or neutered under one year of age grew significantly taller than non-sterilized dogs or those not spayed/neutered until after puberty. And the earlier the spay/neuter procedure, the taller the dog. This is significant because fast skeletal growth may lead to disease of the ends of the long bones.

Diseases other than cancer made the research summary paper.  Here are those of most concern.  A study on canine cruciate ligament (CCL) injuries concluded that spayed and neutered dogs had a significantly higher incidence of CCL rupture than their intact counterparts. While large breed dogs had more cruciate injuries, sterilized dogs of all breeds and sizes had increased rupture rates.

Hip dysplasia is so common everyone has heard of it.  In a study conducted at Cornell published in the Journal of the American Veterinary Medical Association, the results showed that both male and female dogs sterilized at an early age were more prone to hip dysplasia.

The list goes on, much longer than I have space here to explain.  But here is a quick look at some of the other issues that are suspected to be caused by “early spay and neuter”.

Data shows that in the early neutering male dogs

  • If done before 1 year of age, significantly increases the risk of osteosarcoma (bone cancer); this is a common and very aggressive cancer in medium and large breed dogs.
  • increases the risk of hemangiosarcoma by a factor of 1.6
  • triples the risk of hypothyroidism
  • increases the risk of progressive geriatric cognitive impairment (CDS)
  • triples the risk of obesity, a common health problem in dogs with many associated health problems

Data shows that in the early neutering female dogs

  • if done before 1 year of age, significantly increases the risk of osteosarcoma (bone cancer)
  • increases the risk of splenic hemangiosarcoma by a factor of 2.2 and cardiac hemangiosarcoma by
  • a factor of >5; this is a common cancer and major cause of death in some breeds
  • triples the risk of hypothyroidism
  • increases the risk of obesity by a factor of 1.6-2, a common health problem in dogs with many associated health problems
  • causes urinary “spay incontinence” in 4-20% of female dogs
  • increases the risk of persistent or recurring urinary tract infections by 3 to 4 times

You can also find mention of increased incidence of behavioral problems including: Noise phobias, Fearful behavior, Aggression, Undesirable sexual behaviors.

IMPORTANT: As responsible members of society, we owe it to our communities to proactively protect our intact pets from unplanned breeding at all costs.

How seriously you take your responsibility as a pet owner is the biggest determining factor in how risky it is to leave your dog intact until he or she matures. If you are responsible enough to absolutely guarantee your unsterilized pet will not have the opportunity to mate, I would encourage you to wait until your pet is past puberty to spay or neuter.

If you are unable to absolutely guarantee you can prevent your dog from mating and adding to the shameful, tragic problem of pet overpopulation, then I strongly encourage you to get your animal sterilized as soon as it’s safe to do so.

I’m not advocating pet owners keep their dogs intact indefinitely. I’m also not suggesting that shelters and rescues stop sterilizing young animals before re-homing them. Shelter organizations can’t determine how responsible adoptive pet owners will be. In this situation, the risk of leaving adoptable animals intact is simply unacceptable. Shelters and rescues must immediately spay/neuter pets coming into their care.

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Dr. Jim Humphries has been a veterinarian for 40 years and provides hospice and end of life care for pets in the Colorado Springs area.  He has served in the US Army Veterinary Corps, and as the veterinarian at CBS News and CNN. He is a consultant for several veterinary pharmaceutical companies. In addition to practice, he also serves as a Visiting Professor at the College of Veterinary Medicine at Texas A&M University.www.HomeWithDignity.com.  

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