spay your dog

Last year I had to say good bye to my dog, Maddie.

Maddie had come to me 6 years earlier—dumped in the waiting room of the hospital where I worked when our receptionist had her back turned.  She was emaciated, matted, and full of fleas.  Her teeth were rotting, she was not spayed and she had several large tumors on her belly.  Even though our town shelter is low-kill, she likely would have been euthanized because of her medical conditions.  I took one look at her and knew I couldn’t let that happen.  She and I were bound together from that very first moment.

My colleagues helped me nurse her back to health.  She was groomed, she had a dental cleaning, she was spayed and her masses (all confirmed benign mammary tumors) were removed.  She couldn’t walk half a block without needing to be carried, but with time and care she began to run and she could soon leap over a tall building (or at least a small ottoman) with a single bound.

Over the next 6 years Maddie was my constant companion.  She came to work with me every day, visited my grandmother in the nursing home with me and joined me when I baby sat my niece.  She was with me as I moved into my apartment to live on my own for the first time.  I would have done anything for her including nursing her though a gallbladder removal surgery and 5 more mammary mass removals.  Most of the tumors were benign, one was precancerous, one a low grade cancer she survived…and lastly, the one that killed her.  She died within four months of diagnosis despite working with an excellent veterinary oncologist who recommended and provided her with the best care available.

spay your dog


I am biased.

The reason I tell you all of this is in the interest of full disclosure.  There is a debate these days about when to spay your dog. If Maddie had been spayed at the traditional age of 6 months, she might still be alive—she definitely wouldn’t have gone through the agony and convalescence associated with 6 painful surgeries.  So maybe I’m not the best person to ask for input on this conversation.  I’m too emotionally involved.  I’m going to try to put my personal feelings aside though and break it down by the numbers.  I’ll try not to bore you.  (And in the spirit of not rambling on forever, I’m going to limit the discussion to female dogs for this particular article)

Mammary Cancer

The original studies show that spaying a dog before she goes into heat virtually eliminates her chances of getting mammary tumors.  Each heat through the third dramatically increases the risk of developing a tumor. After that, the damage is done.  We can also do some modern day comparisons.  In America, the majority of dogs are spayed and the incidence of mammary tumors is very low.  Most European countries are against elective spaying and neutering.  In these countries, as many as 70% of all tumors in female dogs are mammary tumors.  Now, not all of these are cancerous—in fact, statistically, only half are cancerous, and half of those that are can be cured with surgery.  Even still, that means that 25% of mammary tumor are potentially fatal.  And that means that if spaying were universal, you could hypothetically decrease the risk of a life threatening tumor by as much as 17%.

The Golden Study

The mammary cancer stats have guided veterinarians for a long time, but a big shift in perspective came about after the release of a report from UC Davis in 2013.  This study retroactively took a look at the incidence of 3 types of cancer (lymphsarcoma , hemangiosarcoma, and mast cell tumors) and 2 types of orthopedic conditions (hip dysplasia and cruciate injuries) in golden retrievers. The study showed that animals that were spayed early were significantly more likely to develop lymphosarcoma and joint problems than animals spayed late or not at all. The increase in lymphoma risk for early spayed females was 4 times that of unspayed females.  For hemangiosarcoma and mast cell tumors, dogs spayed after a year of age were the most likely to be affected, but the dogs who were not spayed at all still fared better than the early spayed dogs.

The evidence seems pretty damning—right?  Not spaying your dog significantly decreases their odds of getting some very serious medical conditions.

Not so fast.  While important, the study has its limitations.  For starters, it only looks at Golden Retrievers.  Dogs who are already at high risk for these diseases.  It also only looks at dogs of a certain age (1-8 years old) who had been voluntarily brought in to a referral hospital, and it only looks at a few diseases.  It’s a start, for sure, and something to take into consideration, but making potentially life altering decisions for our pets based on only this is probably not the best idea.  We need more information.

spay your dog

Expanding the Research

So another study was done.  This one looked at both Golden Retrievers and Labrador Retrievers.  Again, this study was done by looking at the records of pets seen at the UC Davis teaching hospital.  The results for Goldens were comparable to the previous study.  The results for Labs also showed an increased risk of hip and knee problems in spayed dogs, but to a lesser degree than in the Goldens that were studied.  Cancer, however was a different story.  Spaying Labrador Retriever’s seemed to have no effect on their incidence of developing any of the studied types of cancer.

So from this, it seems that there are some breed differences when it comes to the effects of spaying, but it still looks like not spaying your dog is better than spaying them, right?  Even if Golden Retrievers turn out to be the only dogs that are more likely to get cancer when they’re spayed, we should still want to avoid spaying them to prevent joint problems.

But I’m still not sure we have the whole picture.  Small dogs for one thing, are not really known for having these joint problems, so do these findings relate if you have a Yorkie or a Shih Tzu?  Plus, there is the question of whether dogs who are being seen at a referral hospital in one city can be expected to represent all dogs everywhere, including those that do not have the luxury of receiving potentially expensive, gold-standard medical care?

The Big Picture

Well, good news.  Banfield, a veterinary corporation with hundreds of facilities all over the country, went through their databases to study the effects of spaying among other things.  This report, which came out in 2013 looked at over 2.2 million dogs.  Their data showed that in female dogs, spaying increased their life-spans by 23%.  That could mean an extra 2-3 year with your beloved pet.

Of course, it wouldn’t be fair for me not to poke holes in this study, just like I did the others.  For starters, this is just looking at life-span, not specific diseases. Helping our pets live longer is a main objective that most pet owners and veterinarians have, but we also want our pet’s to live better.  Hip dysplasia may not kill but the impact of pain and mobility issues on our pets quality of life should not be under-valued.  Also, this study looks at dogs who receive differing levels of medical care—not all of it necessarily great.  Maybe unspayed dogs in this study are not living as long because the owners choosing not to spay them are also not vaccinating, not protecting against heart-worm and are letting them roam the neighborhood.

Another study in 2013, the Hoffman study looked at over 70,000 dogs of different breeds compiled from teaching hospitals all over North America.  It also showed that dogs that were spayed and neutered had longer average life-spans than intact dogs.  This study also looked at cause of death.  Spayed and neutered dogs were more likely to die of cancer but less likely to die of infections. Again, the unspayed dogs may have been more exposed to infections and hazardous conditions than the spayed dogs.  So the age benefit may not have been caused by spaying, but might just be a correlation.

So when should you spay your dog?

You can see why it’s so hard for us vets to agree. Spaying decreases the risks of some health problems and increases the risks of other.    There are no straight answers, so for now, I guess I can get away with being biased.  You can evaluate the evidence and use it to help you decide what’s right for your pet, but until I see evidence that convinces me  the decreased risk of mammary cancer is outweighed by the increased risks of other cancers, I say spay your dog and do it early.  I wouldn’t wish what I went through with Maddie on anyone.

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