Does Spaying or Neutering Change Dog Behavior?

Why “fixing” your dog may not fix the behaviors that you find problematic.


If you are wondering, “Does spaying or neutering change dog behavior?” The short answer is, “Don’t hold your breath.”

Decades ago, most shelter workers and veterinarians – and many professional dog trainers, too – believed that gonadectomy (surgical removal of the testes in males or ovaries in females) would not just help prevent the birth of unwanted puppies, but also help alter the behavior of dogs.

Note: Debates over medical issues related to spay/neuter surgery are discussions for another day. Here, we’re looking only at how spay/neuter practices affect canine behavior.

It was widely believed that some of the dog behaviors that humans least appreciate (such as aggression, roaming, humping, and more) could be prevented or resolved through spay/neuter surgery.

Today, though, we have the advantage of more and better research into canine behavior. We also have more experience with a population of dogs that possesses the historically highest percentage of spayed/neutered individuals ever (an estimated 70% to 85% of the dogs in the U.S. have experienced a gonadectomy). This combination has led to a reexamination of many beliefs about canine behavior, and many that were regarded as gospel in the 1970s and ’80s are being revealed as myths. We now know that the behavioral benefits – to us! – of canine sterilization are very limited and should not be treated as a panacea for canine behaviors that many owners find problematic.

Dog Behaviors That Humans Tend to Dislike

Dogs are a charismatic, intelligent, social species. They have willingly joined us in our lives, and in return for their companionship and service, we’ve given them privileged spots in our society, homes, couches, and even beds. Despite this closeness, there are many natural and normal behaviors that dogs exhibit that we tend to dislike, including:

  • Aggression (toward other dogs or humans)
  • Barking
  • Excessive excitability
  • Humping
  • Pulling on leash
  • Roaming
  • Urine-marking

Somewhere along the way, many of these canine behaviors came to be blamed on the hormones that circulate in reproductively intact dogs – particularly male dogs. This was not such a stretch, since humans have long castrated male horses and cattle in order to make them more docile.

In the 1970s, as America woke up to the problem of pet overpopulation and the senseless killing of “surplus” dogs, shelter workers and veterinarians alike began to promote spay/neuter surgery in a population-control effort. As spay and neutering became more common, it began to be regarded and promoted as potentially helpful for reducing some of those behaviors that many owners found inconvenient or distasteful. This multi-benefit sales pitch helped convince owners to “de-sex” their dogs, though it was perhaps oversold based on anecdotal reports from owners, trainers, or vets who found altered animals easier to deal with.

Canine Behavior Research

Anecdotal evidence can often convince people that something is true well before scientists have a chance to test the popular assumptions for accuracy. Some of the most commonly held assumptions about dog behaviors that can be altered or improved (from the human standpoint) through surgical gonadectomy have to do with canine aggression. Many dog owners believe some variation of the following statements:

  • Dogs should be spayed or neutered because sex hormones cause unnecessary stress and aggression.
  • Many aggression problems may be avoided by early neutering.
  • Male dogs display hormonally influenced aggression toward each other. Neutering eliminates much of this behavior.

The problem is, that studies conducted by behavior scientists contradict all of these statements, which now must be considered as persistent but untrue myths.

Behavior scientists in both clinical and research settings have done some of this work. But the development and analysis of large populational surveys have also enabled researchers to address some of the most stubbornly held myths about dog behavior. Two tools that were developed to measure behavior and “behavior problems” in dogs have proven to be particularly useful for this purpose.

The first is the Canine Behavioral Assessment and Research Questionnaire (C-BARQ), a standardized behavioral evaluation tool developed and validated by Yuying Hsu and Dr. James Serpell at the University of Pennsylvania in 2003. C-BARQ is an owner-completed survey that has been available for public access online since 2005. Today, the C-BARQ database contains detailed behavioral evaluations for more than 50,000 pet dogs, comprising more than 300 different breeds and cross-breeds. The survey contains 100 questions about an array of dog behaviors that have been grouped into categories such as aggression, fear, and anxiety.

Another researcher, Dr. Parvene Farhoody, analyzed a set of the C-BARQ data involving some 10,839 dogs in her master’s thesis for Hunter College in 2010.

The results of these two studies were supported by the later findings of a 2018 study from a research team headed by Paul McGreevy of the Sydney School of Veterinary Science at the University of Sydney (Australia), with another 9,938 dogs.

All of these studies were in agreement: Sterilized (spayed or neutered) dogs are more likely to show an increase in aggressive behaviors as a result of spaying and neutering, rather than the long-touted decrease. The amount of the increase varied depending on the type of aggression presented (toward the owner, toward strangers, toward other dogs, etc.), ranging from about a 20% increase to more than twice the level of aggression observed in unsterilized dogs.

According to the data, neutered male dogs are more likely to be aggressive toward intact males than intact males interacting with other intact males. And female dogs spayed later in life are less likely to show an increase in aggression than females who were spayed at a young age.

The Dog-Owning Public is Invited to Participate

The C-BARQ was originally designed to measure the prevalence and severity of behavioral problems in privately owned and working dogs, and that remains its primary value and purpose. You can investigate the C-BARQ data, or use the tool to analyze your own dog’s behavior (and enter his personality assessment into the C-BARQ data to be used in future behavior studies).  After you complete the questionnaire, you can compare your dog’s scores to canine population averages in categories including aggression, fear, anxiety, attachment, and more.

Go to:

Other Canine Behavior Myths Busted

There are other, less specific myths about the effects of canine spay/neuter practices that have been called into question through the analysis of the C-BARQ data, including:

  • Spaying and neutering make pets better, more affectionate companions.
  • Unsterilized animals often exhibit more behavior and temperament problems than do those who have been spayed or neutered.

In fact, the UPenn researchers found a roughly 31% increase in fearfulness for both genders after sterilization, a 33% increase in touch sensitivity, and an 8% increase in excitability. This seems to belie the argument that spaying and neutering make for better, more affectionate companions. While we must always remember that correlation doesn’t necessarily mean causation, these are, indeed, significant correlations.

It would be worth considering other correlations, such as the age of the dog at the time of surgery. How many dogs are perhaps sterilized during an adolescent fear period, which might contribute to an increase in fearfulness and touch sensitivity? How might the proliferation of puppy mill puppies born to mothers housed in stressful environments contribute to a greater likelihood of the development of fear, touch sensitivity, and excitability following spay/neuter surgery?

On the bright side, neutering does appear to reduce urine-marking behavior and decreases roaming behavior by intact males pursuing females in season.

Still Good Reasons for Spay/Neuter

Gonadectomy prevents the proliferation of puppies for whom there may not be homes, and the widespread prevalence of the practice has definitely helped to reduce the senseless, “accidental” production of unwanted puppies and the deaths of healthy, adoptable dogs by many millions annually. Just don’t think spaying or neutering your dog is going to prevent or solve all of his or her behaviors that you find problematic. Statistical analysis of a huge population of spayed and neutered dogs says that it won’t.

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Pat Miller, CBCC-KA, CPDT-KA, grew up in a family that was blessed with lots of animal companions: dogs, cats, horses, rabbits, goats, and more, and has maintained that model ever since. She spent the first 20 years of her professional life working at the Marin Humane Society in Marin County, California, for most of that time as a humane officer and director of operations. She continually studied the art and science of dog training and behavior during that time, and in 1996, left MHS to start her own training and behavior business, Peaceable Paws. Pat has earned a number of titles from various training organizations, including Certified Behavior Consultant Canine-Knowledge Assessed (CBCC-KA) and Certified Professional Dog Trainer - Knowledge Assessed (CPDT-KA). She also founded Peaceable Paws Academies for teaching and credentialing dog training and behavior professionals, who can earn "Pat Miller Certified Trainer" certifications. She and her husband Paul and an ever-changing number of dogs, horses, and other animal companions live on their 80-acre farm in Fairplay, Maryland.


  1. Well, you had me applauding until the very end. Since there are sterilization methods available and approved by the AVMA for dogs, there is no good reason to de-sex them. Besides the behavioural issues, there are significant issues of metabolism, cancer, and orthopaedics. Albeit the purpose of the article was not to bring these up, I nevertheless cannot help but think of them at once. Overall, in my own breed (golden retrievers) for sure, the dogs are far better off being hormonally intact. There can be instances where gonadectomy is necessary, but these are rare. I wish these procedures were illegal here, as they are in Norway.

  2. I’m hopeful that more vets in the US will familiarize themselves with sterilization techniques that leave the dogs hormonally intact. For example, vasectomy for males, ovary-sparing spay for females. I’ve lived with two intact male dogs (still have one of them) and all of the frustrations I have around his intact status are about other dogs (neutered males going after him) and owners who assume he’s aggressive because he’s intact.