Think Before You Spay or Neuter

As a veterinarian, the recommendation to spay/neuter pets has always been very simple – do it, and the sooner the better.  Having worked at an animal shelter for five years, I was good at sterilizing animals as young as two months of age. It was important that animals were “fixed” before they left the shelter because any animal that is not sterile is a possible source for more unwanted pets.

Spaying and neutering involves the surgical removal of a pet’s ovaries and uterus (spay) or testicles (neuter). We have all been taught that this procedure helps thwart many health, behavioral, and population problems. However, recent research is refuting the health benefits of spaying and neutering. Now, making the decision whether or not and when to spay/neuter is much more complicated.

A 2012 study concluded that sex hormones promote certain cancers and that the increased risk of mammary cancer in unspayed females has not been scientifically proven.  In 1999 a study found that spayed females had five times more risk of developing heart tumors than intact females, while neutered males had a slightly increased risk over unneutered males. In 2002 research showed that neutered males were four times more likely to develop prostate cancer than intact males.

More research in 2002, this time involving 683 Rottweilers, discovered that those that were spayed/neutered were significantly more likely than intact dogs to develop osteosarcoma (bone cancer). A 2007 study found that neutered male dogs were much more likely to develop prostate and bladder cancer than unneutered males. In 2009, a study found that spayed females were more likely to develop lymphoma (cancer of the lymph nodes) than unspayed females.

Research done on 759 Golden Retrievers on 2013 found that neutered males were two times more likely to have hip dysplasia than unneutered males. Also, intact males and females in the study had no ACL (Anterior Cruciate Ligament) ruptures, while 5% of neutered males and 8% of spayed females did.  Neutered males were three times more likely to contract lymphoma than unneutered males. Mast Cell Tumors and Hemangiosarcoma (cancer of the blood vessels) were more common in spayed females than in those that were unspayed.

Just to further muddy the water, a study of over 40,000 dogs in 2013 found that spayed/neutered dogs lived longer, on average 9.4 years while intact animals lived 7.9 years. Since the study only looked at cases referred to a teaching hospital, the results may not reflect the “real world” and may simply be an indication that people who do not spay/neuter their pets are less conscientious caregivers.

Finally, a study published in 2014 of 2,505 Vizslas born between 1992 and 2008 found that spayed/neutered dogs were more likely to develop all cancers or behavior problems, including fear of storms. (Links to each of these studies can be found on my web site:

There are flaws in every study studies cited.  No single piece of research ever should be looked at as conclusively proving anything. On the other hand, the weight of research now indicates that sterilizing pets is not as innocuous as most people (and vets) think. Time seems to have shown that when you upset the intricate balance of the endocrine system by removing the source of sex hormones bad things can happen to the overall health and longevity of our pets.

We have known for decades that sterilizing immature pets delays the closure of their bones’ growth plates, causing the bones of the legs to grow abnormally long. The thing we’re just now realizing is that extra-long bones can throw off the biomechanics of the legs, apparently leading to an increased risk of ACL ruptures and hip dysplasia. It is also becoming apparent that the upsurge in cancer we have been seeing in pets may, in part, be due to us inadvertently screwing up their hormonal balance.

I AM NOT SAYING THAT YOU SHOULD NOT SPAY/NEUTER YOUR PET.  It can be difficult to manage an unspayed female since a male dog can smell a female in heat from two miles away. Unneutered male dogs sometimes develop aggressive behaviors and might run away to pursue females in heat. Plus, we live in a world where pet overpopulation is a huge problem. Millions of animals are killed at shelters every year because there are not enough loving homes for them all.

So what’s the answer? One size does not fit all. If you have a female dog I would recommend that you consider delaying the spay surgery until she is one to two years old, but if and only if you can handle the responsibility of keeping her from reproducing. This will give her body the benefit of fully maturing before the hormones are removed.

For male dogs, I now have an even better solution than delaying neuter surgery: skip the surgery and have your pet chemically altered. I have available at Beaver Animal Clinic the only FDA approved, injectable neuter technology called Zeuterin.  “Zeutering” a dog involves injecting into each testicle a small amount of a solution that selectively kills the cells that produce sperm. I know, it is hard to imagine an injection into the testicle (at least for men that image is difficult). However, light sedation and post-injection pain meds are all that are needed. There is no general anesthesia and no incision as with surgical neutering.

The best part is that the Zeutered dogs maintain about 50% of their normal testosterone levels. This is less than normal, but much better than the zero testosterone level left to neutered dogs. Long term studies have shown that 10 years post injection Zeutered dogs have no injection-site side effects.  The process is 99.6% effective at sterilizing the dog.

Zeutering is currently approved for dogs between three and ten months of age. Beaver Animal Clinic is the only veterinary facility in the Pittsburgh area to have this cutting edge procedure available (and it doesn’t even involve any cutting). Using this new neutering process will lead to adult male dogs with a more normal balance of hormones and all the health benefits that brings.


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