“Neutering” is the medical term for spaying a female or castrating a male dog or cat. There are many ways to perform neutering for companion animals, and in most cases, all reproductive organs are removed.
Neutering began as an effort to combat pet overpopulation and increase health benefits. And while neutering dogs can decrease the risk of ovarian and breast cancers, prostate disease, and pyometras, it can also decrease or even eliminate socially unacceptable behaviors in dogs.
Neutering is the scientific term for removing the reproductive organs of an animal. It’s commonly referred to as “spaying” for female dogs and “castration” in males.
The procedure is performed by a licensed veterinarian and is considered a routine preventative procedure. Along with preventing unwanted dog pregnancies and litters, neutering can prevent clinical illnesses including:
Neutering may occur at different ages based on many different factors, such as breed, age, temperament, and how you acquired your pup. Talk with your vet about the best time to neuter your dog.
The Complicated Relationship Between Neutering and Aggression
Are neutered dogs more aggressive? If you’ve been wondering this question as a dog owner, you’re definitely not alone. I’ve heard this concern from countless pet parents who notice behavior changes after their furry friends get “fixed.” The relationship between neutering and aggression is way more complicated than most people think, and the evidence is actually pretty conflicting.
As a dog behavior enthusiast who’s spent years researching this topic, I can tell you that neutering doesn’t have a one-size-fits-all effect on aggression. Sometimes it helps, sometimes it doesn’t, and sometimes it might even make things worse. Let’s dive into what the science actually says about this common concern.
What Exactly Happens During Neutering?
Before we talk about behavior, let’s clarify what neutering actually is:
- Neutering is the scientific term for removing reproductive organs
- For females, it’s commonly called “spaying”
- For males, it’s commonly called “castration”
- The procedure removes reproductive hormones (testosterone in males and estrogen in females)
- It’s performed by licensed veterinarians as a routine preventative procedure
Neutering isn’t just about preventing unwanted puppies. It’s also done to prevent certain health issues like cancer (ovarian, breast, and prostate), hormone-induced diseases, and infections.
The Myth vs. Reality of Post-Neutering Aggression
Here’s where things get interesting. There’s a common belief that neutering automatically reduces aggression, but the scientific evidence tells a more nuanced story.
Evidence Supporting Increased Aggression After Neutering
Several studies have found concerning connections between neutering and increased aggression:
- Neutered males have been found to be more “emotionally unstable” with a greater tendency for aggressive behavior
- Higher rates of owner-directed aggression have been observed in neutered dogs
- Resource guarding (growling over food or toys) appears more common in neutered dogs than intact dogs
- Some studies show neutered males are more likely to be implicated in human-directed growling
- Children hospitalized with resource guarding-related dog bites were statistically more likely to have been bitten by a neutered dog
Evidence Supporting Decreased Aggression After Neutering
On the flip side. other research suggests neutering can reduce certain types of aggression
- Human-directed aggression was less prevalent in neutered dogs in some studies
- Conspecific aggression (dog-to-dog aggression) was reduced in neutered dogs according to some research
- Aggression in male dogs toward other dogs decreased by more than half after neutering
- Territorial marking and roaming behaviors significantly decrease after neutering
What About Fear and Anxiety?
One of the most consistent findings across multiple studies is that neutering might increase fearfulness and anxiety in dogs
- Neutering has been implicated in increasing anxiousness in pet dogs
- Dogs neutered before one year old often show exaggerated fearful responses
- Non-social fear was more likely to be seen in neutered dogs
- Rates of noise phobia were highly represented in neutered dogs
This is particularly important because defensive aggression is often linked to anxiety and fear A dog that’s more anxious might be more likely to react aggressively in certain situations
The Hormonal Connection to Behavior
The key to understanding these conflicting findings lies in how hormones affect the brain and behavior:
The hypothalamic-pituitary-gonadal (HPG) axis is crucial for regulating reproductive function, but it also influences behavior. Sex hormones like testosterone and estrogen aren’t just about reproduction – they act as neuromodulators affecting sociosexual behavior and emotions.
Interesting fact: Studies have found that entire (non-neutered) dogs are generally “bolder” than neutered dogs, with entire males being more confident than entire females. This makes sense when you consider that in humans, higher testosterone levels correlate with increased confidence and resilience.
Different Effects Based on Sex and Timing
The impact of neutering on aggression isn’t the same for all dogs:
Males vs. Females
- Neutered males may show increased stranger-directed aggression
- Spayed females are highly represented in studies of human-directed aggression
- Neutered males are more likely to exhibit resource guarding
- Female spayed dogs appear more likely to show reactive behavior compared to intact females
Timing Matters
When neutering occurs can significantly influence the behavioral outcome:
- Early neutering (before puberty) seems to increase the risk of certain behavior problems
- Dogs neutered before the age of one year show more exaggerated fearful responses
- Delayed neutering (between 7-11 months) resulted in better trainability and reduced reactivity compared to earlier neutering
Common Types of Aggression After Neutering
If you’re seeing aggression in your neutered dog, it might fall into one of these categories:
- Territory aggression: The drive to defend personal space, usually along property lines or in the home
- Resource guarding: Protecting food, toys, or other valued items
- Fear-based aggression: Reacting aggressively due to fear or anxiety
- Redirected aggression: Lashing out at other pets or people when stressed
- Dog-to-dog aggression: Hostility toward other dogs, especially of the same sex
What Dog Owners Should Actually Expect After Neutering
So what should you realistically expect after neutering your dog? Here’s the honest truth:
- Immediate behavior changes are uncommon – Most changes happen gradually
- Some behaviors will improve – Particularly marking, roaming, and mounting
- Some behaviors may worsen – Especially fear-based reactions and anxiety
- Learned behaviors won’t magically disappear – If your dog already has established aggressive behaviors, neutering alone won’t fix them
- Individual variation is HUGE – Breed, age, temperament, and prior experiences all matter
How to Address Aggression in Your Neutered Dog
If your neutered dog is showing aggression, here are practical steps to take:
1. Rule Out Medical Issues
First things first – make sure your dog isn’t in pain or suffering from a medical condition. Pain is a common trigger for aggression.
2. Work with a Professional
Don’t try to solve serious aggression issues on your own:
- Consult with a veterinary behaviorist or certified dog trainer
- Get a personalized training plan for your specific situation
- Be consistent with the training approach
3. Environmental Management
- Create a structured routine for your dog
- Provide plenty of physical exercise and mental stimulation
- Identify and avoid triggers when possible
- Use baby gates, crates, or other management tools to prevent aggressive incidents
4. Positive Reinforcement Training
- Reward calm, non-aggressive behavior
- Teach alternative behaviors for stressful situations
- Practice desensitization to triggers in controlled settings
- Never punish growling (this can lead to biting without warning)
5. Consider Medication if Necessary
In severe cases, your veterinarian may recommend medication to help manage anxiety that could be contributing to aggressive behavior.
Should You Still Neuter Your Dog?
Despite the potential for some behavioral changes, neutering still offers many benefits:
- Prevents unwanted litters
- Reduces certain health risks like cancer
- Decreases roaming, marking, and mounting behaviors
- Can help with some types of aggression
The key is making an informed decision based on your individual dog. For dogs already showing fearful or anxious behaviors, it might be worth discussing alternatives with your vet, such as:
- Delaying neutering until behavioral issues are addressed
- Considering temporary chemical castration to see how your dog responds
- Implementing behavior modification before permanent neutering
The Bottom Line on Neutering and Aggression
The relationship between neutering and aggression isn’t straightforward. Based on the current research, here’s what we can say:
- Neutering is NOT a quick fix for aggressive behavior
- Some dogs may become more aggressive after neutering
- Others may become less aggressive, particularly with certain types of aggression
- Fear and anxiety often increase after neutering, which can lead to defensive aggression
- Each dog is an individual – breed, age, prior experiences, and environment all matter
As a responsible dog owner, the best approach is to:
- Discuss your specific dog’s needs with your veterinarian
- Consider your dog’s current behavior and temperament
- Be prepared to implement training regardless of your neutering decision
- Stay vigilant about behavior changes after neutering
The most important thing to remember is that neutering alone isn’t enough to prevent or treat aggression. Proper training, socialization, and management are essential regardless of whether your dog is neutered or intact.
Have you noticed behavior changes in your dog after neutering? I’d love to hear about your experiences in the comments below!
How Neutering Affects Dogs’ Behavior
Intact dogs (those who have not been neutered) can have a wide range of behaviors that occur due to the fluctuations in their hormone levels. Along with the health benefits, many of the behaviors that people find socially unacceptable in dogs decrease drastically with neutering. This includes:
- Aggression toward other dogs: Aggression in male dogs will decrease by more than half with altering.
- Roaming behaviors: Both male and female dogs have a decreased roaming distance and desire to roam after neutering, which helps reduce the risk of accidents (such as being hit by a car) or getting lost.
- Marking: Neutering a male dog before marking behaviors begin eliminates the behavior to almost 2%. However, if you neuter an older dog who has already begun marking, it might be more difficult or impossible to modify the behavior.
- Mounting, humping, and increased sexual drive: These behaviors are drastically reduced by more than 50%.
These behaviors are reduced because neutering decreases reproductive hormones (testosterone and estrogen) in your dog. But it’s important to remember that, even with neutering, hormones are still present in the body—they just don’t fluctuate as they would with intact reproductive organs.
As with any behavior, there are many influencing factors, and neutering is not the only one to consider. Breed, genetics, susceptibility to certain behaviors, and medical conditions should also be taken into account.
It’s not just undesirable behaviors that are affected by neutering. The risk for weight gain also rises—not because of decreased activity, but because of a biological process that occurs after neutering. A dog might feel hungrier due to changing hormones, but in reality, they need fewer calories than their craving suggests.
Hormonal changes affect both male and female dogs, but as with any procedure, the effects can be different.
- Territory aggression: The drive to defend personal space from friend or foe. This behavior typically occurs along a property line or, sometimes, in your pup’s home. This behavior is rarely seen in puppies and usually occurs as reproductive hormones are released in adolescence.
- Socially unacceptable behaviors: Roaming, marking, and mounting.
- Roaming/escaping: Hormones play a large role in the drive to reproduce, leading dogs to escape to find a partner. Intact dogs not only have a higher chance of roaming but also roam greater distances.
- Marking: This is a distinctive behavior attributed to sexual hormones. It occurs to either show other animals that a dog is seeking a partner or that a partner has been claimed.
- Mounting: This behavior increases with sexual drive and occurs during excitement in many dogs. This behavior becomes more learned the longer a dog is intact.
- Aggression towards other dogs: There are many reasons why dogs display aggression towards other dogs, but sexual hormones play a role in the intensity and duration of these events. Same-sex aggression is higher in male dogs who are not neutered.
- Hyperarousal: This behavior occurs when excitement becomes heightened. Sexual hormones can increase the behavior.
- Resource guarding: As with aggression, resource guarding can occur for various reasons, though it can be more frequent with intact animals.
Keep in mind that, while these behaviors can be modified or even diminished with neutering, some behaviors are learned. Neutering might decrease these behaviors, but completely eliminating them may require behavioral therapy.
Should You Neuter Your Dog?
Neutering dogs and cats is the only way to completely prevent unwanted pregnancies. But more than that, the procedure also improves the overall health and behavior of your pet.
When considering whether to neuter your dog, talk with your veterinarian. Your vet can help conduct a risk assessment and will work with you to determine your dog’s risk factors so you can address health and behavior concerns.
Featured : Adobe/MeganBetteridge
Dr. Tiffany Tupler is a graduate from the University of Florida College of Veterinary Medicine with a certificate in shelter medicine and…
Intact dogs are no more aggressive than others, but other factors need to be taken into account
FAQ
Does neutering cause aggression in dogs?
There is a common misconception that neutering can cause aggression in dogs. However, this belief is not supported by scientific evidence. In fact, research has shown that there is no direct link between neutering and aggressive behavior in dogs.
Does neutering a dog help curb aggressive behavior?
Neutering, also known as spaying or castration, is a common surgical procedure used to sterilize male dogs. While neutering is primarily done to prevent unwanted litters and reduce the risk of certain health issues, many dog owners also wonder if it can help curb their pet’s aggressive behaviors.
What causes same sex aggression in dogs if not neutered?
Same-sex aggression is higher in male dogs who are not neutered. Hyperarousal: This behavior occurs when excitement becomes heightened. Sexual hormones can increase the behavior.
Does neutering a dog make a difference?
As in previous studies, the new data clearly shows that the positive behavioral effects that were expected from neutering did not occur, and if anything, the behaviors of neutered male dogs tended to be considerably less desirable. Of the 100 behaviors assessed, 40 showed statistically significant differences between the castrated and intact dogs.
Are neutered males more aggressive?
Neutered males have also been found to be more “emotionally unstable”, display a greater tendency for aggressive behaviour (Kaufmann et al., 2017) and exhibit higher rates of owner-directed aggression (Guy et al., 2001; Hsu and Sun, 2010).
Do neutered dogs have behavioural problems?
One large-scale review highlighted that neutered males and females were nearly twice as likely to exhibit behavioural problems (Dinwoodie et al., 2019), and another identified that excessive activity, barking and aggression are more prevalent in neutered dogs (Chung et al., 2016).
Are male dogs more aggressive after neutering?
Are dogs more aggressive when not neutered?
Does neutering of dogs make them more less aggressive?
Males neutered early in life are less aggressive toward other males and are not distracted by females in heat.