The Spay / Neuter Decision

In North America in the past, the age to spay and neuter pets was pretty cut and dried - we did everything at 6 months of age, male or female, before our pets reached a reproductive age. This was largely because we had a large problem with "excess pets" ending up in shelters, and the euthanasia rate was high. It was far more humane to try to curb pet reproduction than kill animals in large numbers.

Somehow this phenomenon didn't manifest in Europe, at least, not to the same degree. There, most pets (dogs, anyway) are left reproductively intact. Why is this? Perhaps there are fewer free-roaming dogs there? More responsible pet owners? More tolerance for the behaviours and habits of intact animals? Smaller populations? Someone has probably studied this, but I don't have the answer at the moment.

In any event, we are in Canada, not Norway. The custom is to neuter or spay animals that are not being used for breeding, but this is changing. Especially in the last 10 years, the recommendations are evolving as we have data that tells us how different animals are affected, positively and negatively, by spaying and neutering.

For the sake of saving my fingers, I'm going to use the term "desexing" to refer to either neutering (castration, removal of the testicles) or spaying (ovariectomy, ovariohysterectomy, removal of the ovaries with or without the uterus).

More recent studies in some breeds show that desexing is not always a benign process. We have always known that desexed animals have a tendency to weight gain and don't put on muscle as well as intact animals. Dogs that are desexed before puberty end up longer-legged and less muscular than their intact counterparts. Female dogs that are spayed have an increased risk of urinary incontinence and may need oral hormone therapy. The newer, longer term studies are also telling us that in large and giant breed dogs that are predisposed to hip dysplasia and cruciate ligament disease, desexing before maturity can increase the risk of these orthopedic conditions later in life. There are very specific cancer types in some breeds that are triggered by hormonal changes and the risk of these cancers can increase when hormones go missing.

As in anything statistical, the number really matter. Some of the increased risk are real but tiny. It might increase the risk of one problem from 1 in 250,000 to one in 235,000. Desexing (especially before puberty) might increase the risk of another problem from 1 in 250,000 to 1 in 1,000, which is a much more significant increase. So when we read these studies we have to apply our critical thinking skills to figure out whether the results are just theoretically interesting or interesting and significant to our pets.

Here is a small sampling of the information now available on this topic. Some are more "science-y" than others. Have a browse through them to familiarize yourself with the issues, and have a talk with your veterinarian about the timing of this surgery for your dog.

Current perspectives on the optimal age to spay/castrate dogs and cats (May 2015)

Spay and Neuter Surgery’s Effects on Dog Health (by Dr David Lane, a local specialist in canine rehabilitation and sports medicine)

Assisting Decision-Making on Age of Neutering for Mixed Breed Dogs of Five Weight Categories: Associated Joint Disorders and Cancers (2020)

Assisting Decision-Making on Age of Neutering for 35 Breeds of Dogs: Associated Joint Disorders, Cancers, and Urinary Incontinence

An Ancient Practice but a New Paradigm: Personal Choice for the Age to Spay or Neuter a Dog (2021)