When Should I Spay or Neuter My Dog? How Research Becomes Dogma

Limited spay and neuter findings seem to have become a blanket rule that many embraced almost overnight.

Photo credit: BP Miller

Lately, it feels like almost every new puppy guardian I meet tells me they plan to wait until their dog is one or two years old before having them spayed or neutered.

I hear this from people with large dogs, but increasingly, I hear it from people with small dogs too.

It is remarkable how quickly information from this research has spread, not only throughout the veterinary profession but among the general dog-loving public. For years, six months was treated as the standard age to spay or neuter a dog, in North America anyway. New research challenged that blanket recommendation by suggesting that the potential health effects of neutering can differ according to a dog’s breed, sex, size and age at the time of surgery.

This is a good thing. The more we continue learning about ways we may be able to prevent our beloved companions from developing serious health conditions that compromise their quality of life, the better. This research should have moved us toward more individualized decisions about the best time to spay or neuter each dog. Instead, it feels as though the public have quickly latched on to an overgeneralization and replaced one universal rule with another: never spay or neuter a dog before they are fully grown.

But that is not what the research says.

What Does the Research Say About When I Should Spay or Neuter My Dog?

A 2024 Frontiers publication, Effective Options Regarding Spay or Neuter of Dogs, brings together 16 articles examining the health, behaviour and welfare considerations surrounding spaying and neutering. Several of the included studies used veterinary records to look for associations between a dog’s age at neutering and selected joint disorders, cancers and urinary incontinence. The results varied considerably among breeds and between male and female dogs.

For some breed and sex combinations, neutering at younger ages was associated with a higher incidence of certain conditions. For many others, the researchers did not identify a significant increase at any neutering age. The breed-specific recommendations covered 40 breeds. A separate mixed-breed study found that, among dogs expected to weigh at least 20 kilograms (~ 45lbs.) as adults, neutering before one year was associated with a greater risk of joint disorders. For mixed-breed dogs expected to remain under 20 kilograms, however, the researchers found no increased risk among the conditions studied that supported recommending a particular age. These studies were retrospective. They identified associations in existing veterinary records (from one veterinary hospital), but they could not prove that neutering caused the differences observed.

This is research has value! It gives guardians and veterinarians more information to consider when making decisions for an individual dog. But it does not support automatically waiting until one or two years for every dog. Somehow, nuanced findings about selected breeds and health conditions seem to have been simplified into a universal rule and adopted with astonishing speed.

Why does some evidence face a much higher bar?

The rapid acceptance of recommendations to delay spaying and neutering becomes particularly striking when compared with the dog world’s response to behaviour research.

The American Veterinary Society of Animal Behavior recommends reward-based methods for all dog training, including the treatment of behaviour problems. Its position is that aversive methods, meaning methods that rely on force, pain, or physical or emotional discomfort, should not be used. This recommendation is not limited to a small selection of breeds or based on the findings of a single study.

A growing body of research has repeatedly associated aversive training with greater stress, fear and poorer welfare. Research has also failed to demonstrate that aversive methods are necessary or more effective than reward-based training. Yet shock collars, prong collars, leash corrections and other aversive methods remain widely used and defended.

Studies supporting reward-based training are picked apart and dismissed as biased, flawed or inapplicable. Many people continue to deny the published research and demand more proof while using approaches that carry a known risk of harm to dogs and the people who interact with them.

Why are relatively limited findings about the effects of spaying and neutering on physical health accepted so readily, and even taken beyond what the researchers concluded, while a much broader and repeatedly supported body of behavioural and welfare evidence that has been available for years remains perpetually controversial?

Puppy socialization offers another example

Veterinary behaviour professionals have recommended for years that safe, broad-based socialization before the completion of the puppy vaccination series should be the standard of care. Appropriate disease-mitigation precautions matter, but isolating a puppy until their second or third set of vaccinations can cause them to miss an important developmental opportunity.

This recommendation applies to puppies generally, not only 40 studied breeds or dogs over a particular weight. Still, many guardians continue to be told to keep their puppies home until they are fully vaccinated, or they continue to follow advice they received years ago before we knew better. When we know better, we can do better, and we owe it to our dogs to make the best decisions we can with the information available to us.

Even when early socialization is encouraged, what it means can become oversimplified. There is now a significant push toward making “neutrality” the goal, but neutrality is only one part of preparing a dog for urban life. Puppies need to be set up in ways that allow them to observe passing people, dogs, bicycles, vehicles and other things in their environment without running up to them. But they also need to be given opportunities to learn how to communicate. Social competence develops through active experience.

By interacting with friendly people and dogs, puppies learn to read signals, respond to feedback, regulate their excitement, approach and disengage, and recover from small misunderstandings. They also need opportunities to actively explore different objects, surfaces and environments rather than experiencing everything passively from a distance if we expect them to not be afraid of these things. The goal is not a puppy who loses their mind every time they see a dog or person because they want to go greet them. It is also not a puppy who only observes the world from afar and is then expected to know how to interact with others as they mature.

An adult dog that was properly socialized during their puppyhood and adolescence can cope when a loud bus drives by, interact successfully with people and dogs when invited, explore unfamiliar things with appropriate support, and remain comfortable when interaction or exploration is unavailable. Once again, a nuanced recommendation risks being turned into something overly simple.

Evidence-based care should not mean following only what's convenient

I do not claim to know exactly why these differences in adoption of information exist. Delaying a procedure may simply feel easier than fundamentally reconsidering how one understands and trains their dog. A clear black and white rule may also spread more easily than recommendations that require judgment, skill and a willingness to change our own behaviour. Whatever the reasons, the discrepancy is difficult to ignore.

Limited, breed-specific findings about spay and neuter timing have rapidly changed how many people believe these decisions should be made for all dogs. Meanwhile, broader recommendations to avoid aversive training and begin safe puppy socialization early continue to be challenged, disregarded or treated as matters of personal opinion. Evidence should help us ask better questions, not create new dogma.

The appropriate age to spay or neuter a dog deserves an individualized conversation that considers the dog’s breed, sex, expected size, health risks and living circumstances. The research should neither be dismissed nor stretched beyond what it can tell us. To be the best dog guardians we can be, we must be willing to consider the available evidence consistently, including when it asks us to reconsider practices we have accepted for years.

Why do some findings seem to become universally accepted rules almost overnight while others with a lot more evidentiary support struggle? That is a question worth asking.

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Supporting Research

• American Veterinary Society of Animal Behavior. Humane Dog Training Position Statement. 2021.

• American Veterinary Society of Animal Behavior. Puppy Socialization Position Statement.

• Hammerle, M. et al. 2015 AAHA Canine and Feline Behavior Management Guidelines. Journal of the American Animal Hospital Association, 2015.

• Hart, B.L. et al. Assisting Decision-Making on Age of Neutering for 35 Breeds of Dogs: Associated Joint Disorders, Cancers, and Urinary Incontinence. Frontiers in Veterinary Science, 2020.

• Hart, B.L. et al. Assisting Decision-Making on Age of Neutering for Mixed-Breed Dogs of Five Weight Categories: Associated Joint Disorders and Cancers. Frontiers in Veterinary Science, 2020.

• Hart, L.A. et al. Assisting Decision-Making on Age of Neutering for German Short/Wirehaired Pointer, Mastiff, Newfoundland, Rhodesian Ridgeback and Siberian Husky. Frontiers in Veterinary Science, 2024.

• Vieira de Castro, A.C. et al. Does Training Method Matter? Evidence for the Negative Impact of Aversive-Based Methods on Companion Dog Welfare. PLOS ONE, 2020.

• China, L., Mills, D.S. and Cooper, J.J. Efficacy of Dog Training With and Without Remote Electronic Collars Versus a Focus on Positive Reinforcement. Frontiers in Veterinary Science, 2020.

• Deldalle, S. and Gaunet, F. Effects of Two Training Methods on Stress-Related Behaviours of the Dog and on the Dog-Owner Relationship. Journal of Veterinary Behavior, 2014.

• Ziv, G. The Effects of Using Aversive Training Methods in Dogs: A Review. Journal of Veterinary Behavior, 2017.

About the Author

Jodi Beedell is a Certified Professional Dog Trainer (CPDT-KA) through the Certification Council for Professional Dog Trainers and holds a Certificate in Training and Counseling through The Academy for Dog Trainers. She owns Raising Fido Dog Training & Behaviour Consultants in Calgary, Alberta, and specializes in reward-based training and force-free behaviour development and modification techniques.