The “Quick Fix?”: Neutering As A Treatment For Aggression

The “Quick Fix?”: Neutering As A Treatment For Aggression

Today’s topic is a juicy one with lots of real-life relevance, so I hope you’re excited!  If you’re a dog owner, or someone who works with dogs, how often have you heard some variation of the following:

“My girl has been growling at me over her food bowl lately!  She thinks she’s the queen of the house.  I really need to have her spayed and nip this in the bud.”

“Oh, your dog is barking and lunging at other dogs on walks?  And he’s intact?  Well, there’s your problem…”

“My dog bit a friend of mine who was visiting last night… it’s so upsetting.  My vet said we need to neuter him ASAP or this will keep happening.”

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As a veterinarian, I can tell you that this line of reasoning is extremely common.  We frequently see clients who schedule their dogs to be spayed or neutered in an effort to resolve a wide variety of behavior issues – usually some type of aggression, but also anxiety issues, training problems, and general “stubbornness.”  Many of my behavior clients specifically ask about this as a potential treatment option, if their pet happens to be intact.

And really, it’s not hard to see where this idea comes from.  It almost feels like common sense, doesn’t it?  We tend to associate testosterone with more aggressive behavior, especially in males.  Less testosterone should equal more docile behavior… right?

The other major factor, unfortunately, is that a lot of dog behavior advice in the media and popular culture still has a tendency to pin most behavior issues on dominance, or conflicts over social status – so it makes a certain amount of sense to think that by spaying or neutering the dog and “taking them down a notch” in the pecking order, we might be able to fix the problem.

So what does the science say?  Is this a worthwhile recommendation that we should be making, or not?

The answer might surprise you.

The truth is, there is very little evidence to support the idea that spaying or neutering is an effective strategy for reducing aggression in dogs.   Most controlled scientific studies on this question (and there have been many!) show that whether a dog is spayed or neutered has no impact at all on the likelihood that they will be aggressive in any given circumstance.

As an example:

Earlier this year, a major study of more than 13,000 dogs ¹analyzed the effect of spay/neuter status and age that the procedure was performed on three different types of aggression – towards familiar people, strangers, and other dogs.  (This is a huge sample size, and the study was very detailed – I highly recommend reading the paper for yourself if this is something that interests you!)

By and large, no significant effects were found.

Interestingly, under one type of statistical analysis, the researchers actually found a modest increase in the risk of aggression (towards strangers, specifically – no change in the other categories) in male dogs neutered between the ages of 7-12 months.  The authors discuss some possible reasons for this finding and acknowledge that we don’t have enough information yet to know if this is a real effect vs. a statistical fluke of some kind, but it’s not the first study to show similar results.

Bit of a shocker, right?

It has been theorized that, if there is actually a true increase in the incidence of aggression in spayed/neutered vs. intact dogs, this could be due to the reproductive hormones having some kind of modulating effect on behavior.

But really, the jury is still out.  I don’t think we have enough evidence at this point to say whether or not spay/neuter status increases risk, although I’m very interested to see further studies on this topic in the future.

I AM comfortable, however, saying that spaying or neutering your aggressive dog is not likely to solve the problem.

And honestly, when you stop and consider what we know about aggression and its underlying causes in dogs, this shouldn’t surprise us at all.  The vast majority of aggressive behavior in pet dogs is related to anxiety, stress, or frustration – not social status.  Effective treatment for these issues is based on addressing the dog’s fear or discomfort through classical conditioning, and/or using reward-based training to teach a different behavioral response to the trigger.

Its gonads, for the most part, aren’t relevant.

Now, there are a few notable exceptions to this rule – namely intact males who consistently have trouble getting along with other males, and female dogs who only show aggressive behavior during their heat cycles.  In these cases, spaying or neutering can absolutely be helpful!  But for most dogs with more run-of-the-mill aggression issues (leash reactivity, resource guarding, biting visitors, etc.), it probably won’t make any difference.

Which begs the question: does all of this mean that you shouldn’t bother having your dog “fixed”?

No, not at all!  There may be many other valid reasons to consider altering your pet.  Even though it’s not likely to help with aggression, there are other behavior problems that do respond well to spaying or neutering in many cases – including urine marking, excessive mounting or “humping” behavior, and roaming.  Having your dog altered also prevents accidental matings, which one could argue is especially important in dogs with significant behavior issues, as these dogs should not be bred.

From a medical standpoint, spay/neuter is a thorny issue.  Potential advantages include prevention of mammary cancer and pyometra (a life-threatening uterine infection) in females, and prevention or reduced risk of testicular cancer, benign prostatic hypertrophy, and perineal hernias in males.  However, there is also growing evidence that altered dogs may be at an increased risk of developing orthopedic problems and certain types of cancer, especially if the procedure is done before they’re fully grown.

The take-home message?

My personal feeling is that the decision to spay or neuter your dog should be made on a case-by-case basis after discussion with your veterinarian.  There are valid pros and cons for every situation.  Just don’t expect it to fix your dog’s aggression issues.

Chances are, his testicles aren’t the problem.


1: Farhoody, Parvene et al. “Aggression toward Familiar People, Strangers, and Conspecifics in Gonadectomized and Intact Dogs.” Frontiers in Veterinary Science. (2018)

19 thoughts on “The “Quick Fix?”: Neutering As A Treatment For Aggression

  1. This is a great article. Quick question. I agree with all that you are saying. I have, however, had the belief that testosterone acts as a “facilitator” of aggression. Testosterone can result in aggression occurring faster and remaining higher for longer periods. Opinion?

    1. That’s a great question! You’re right that there is evidence in multiple species to suggest that testosterone can enhance existing aggressive behavior, at least in some cases – meaning we might expect an intact male dog to have a faster or more intense aggressive reaction to a given situation than a neutered one, all things being equal. BUT – it doesn’t really play a role in determining whether any aggressive behavior is present in the first place.

      In dogs, we know that the possible underlying reasons for unwanted aggressive behavior in any given case are quite complex, and can be influenced by a number of environmental and genetic factors. So while it’s plausible to think that testosterone might have some role to play – at least in theory – it’s so overshadowed by other, more significant factors that it just doesn’t seem to have much practical effect.

      But again, a very interesting question. Thanks for bringing it up!

  2. Our male standard poodle started showing dog aggression (except with our older female poodle) when he was seven months old. We worked with a behaviorist for several months on counter-conditioning with only moderate success, so she suggested neutering. We had not planned to have him neutered because we’d seen studies about possible health benefits for intact dogs, but we did have him chemically neutered when he was ten months old The “zeutering” made him infertile but preserved approximately 50% of his testosterone. There was no change in his behavior, so when he was one year old, he was castrated. He’s four now, is still dog aggressive. There’s no way to know for sure that the procedure didn’t alleviate at least some of the problem, but it certainly didn’t cure it. He’s never shown any human aggression or other problem behaviors, so I wish we hadn’t had it done.

    1. Thanks for sharing your experience with this topic! I do find that many dog owners, as well as some trainers and veterinarians, are more inclined to neuter for inter-dog aggression issues vs. other types of aggression. And in certain specific cases, anecdotally, it can be helpful.

      But more often, in my experience, there’s no noticeable effect one way or the other – so I definitely think that owners need to carefully consider the pros and cons of neutering for their individual dog before choosing to do it.

  3. Interesting. My experience has been equine vs. canine. I really thought there would be a more dramatic, positive correlation since there is such a huge degree of differences after altering in the majority of stallions vs. geldings in ease of handling, etc. (Not all of course… but most). Our dogs are all altered due to the fact that they are all mixed breed rescues that should not be repopulating the dog supply, so hadn’t considered aggression as a factor in our decision, but interesting that the two species would be so different.

    1. That IS interesting, isn’t it? A veterinarian friend of mine who does lots of horse work made the same comment, when I told him what I was writing about this week. I will freely admit that I’m not a horse expert, so I don’t know why things are different – but I’ve always heard from “horse people”, and found in my own limited equine experience, that stallions are generally more aggressive and difficult to handle than geldings.

      An area that I would love to learn more about, for sure!

  4. Great post! As someone who had a human aggressive dog, neutering was recommended to me several times by people who didn’t want to see the truth. After seeking help, training and advice both medical and behavioral for almost two years, his behavior continued to worsen. To make a long sad story short, I found it very frustrating at the time that neutering him was suggested as the solution. My thought at the time was, as you stated, his issues were not toward other male dogs. His issues were directed at humans almost exclusively. I felt at the time neutering him would do nothing toward solving his issues, and I had read that it could possibly make it worse if his behavior was motivated by fear. Truth be told, I do prefer to keep my dogs in tact at least until they are full grown. With mastiffs, this is very important for their growth. That said, I would have neutered my boy in a second had I thought it would make a difference in the outcome.

    1. Agreed that in giant breed dogs, there are lots of good medical reasons to avoid neutering when possible – at least until the dog is fully grown. In your boy’s case, I would also agree that there’s no reason to think neutering him would have been helpful in treating his human-directed aggression issues. But it’s very common advice, all the same.

  5. Excellent post, thank you. I am a supporter of waiting, at the very least, until a dog is mature before neutering, however, your comment, “….that the decision to spay or neuter your dog should be made on a case-by-case basis after discussion with your veterinarian” is not always the best advice. I have felt pressured by vets to spay early (under 12 months) and have felt I have had to justify my decision to wait. Since I am a very responsible owner I find this pressure disappointing from the veterinary profession.

    1. Glad you enjoyed the post! I’m sorry that you felt pressured by your veterinarian to make a decision that you felt wasn’t in your dog’s best interest. Ideally, our job as vets should be to present the pros and cons of spay/neuter surgery at different ages, and then respect whatever the owner decides.

  6. Great blog!! I work in a animal health clinic. I’ve been for 13 years. I’ve never seen a neutering or spaying solve the aggression problem. I think, and that’s my point of vue, if there was less puppy mills, and pseudo breeeders would stop separating puppies at a young age, the mothers would have time, if they have the skills, to give them a better education. I adopted my dog at 1year and 4 months, amstaff mix boxer. His first owner had planned to have him fight but he wasn’t aggressive enough, so he was planning to have him euthanize. A good samaritan took him out of there, and I ended up adopting him. For 5 years, I’ve been working on him and with him to correct some behavior problem. He was scared of alot of things, wind, flying object, tarpel covering bikes or others stuffs. garbages bags, … name it all!!! He through me on the sidewalk a couple times because once of sudden he would see something that would startle him. Today, he participate to parades and walks of all kind. We walk near big construction trucks and he doesn’t get scared anymore but it took me 4 years of hard work and love. He’s my best friend. The best dog I ever had. I just want to say that some dogs that have behavioral problem might come from a low socialization background because he was taken away from his mother and siblings too early. We need better laws to control good breeders. And we have to stop buying dogs from petstore and internet, and start visiting and encouraging good breeders. Thank you Lyne

    1. I’m glad you enjoyed the post! It’s definitely true that poor socialization during puppyhood and early separation from mom and littermates can predispose dogs to developing a variety of behavior problems later in life. Good breeders pay attention to this, and do their best to set their puppies up for success 🙂

      Thanks very much for sharing your thoughts. I agree that these are important considerations for all puppy buyers.

  7. My boy is 2. He has aggressive tendencies, mainly from the previous owners, who rewarded him when he attacked by picking him up and cuddling him. ALL THE TIME.
    He came to me 7 months ago, and have bonded well with him.
    The aggression now is if another dog comes near me, he flies off at them.
    I immediately say NO, I put him down and say BAD DOG. I then ignore him for a few minutes.
    He also gets aggressive towards kids… I say NO, take him on a lead, and put him outside.
    Aggressive towards strangers who go near his bed and toys. Again I say NO, BAD DOG…. and put him outside.
    I hope I am doing the right thing?
    I need some training myself to get him over these problems and I hope that he will grow out of it.
    Cheers
    Libby Simmons

    1. Hi there! I’m sorry to hear that you’re having this problem with your pup.

      You’re asking some great questions here, and it’s really helpful that you’ve been able to figure out the specific situations that seem to trigger his aggression. As far as how to work on the problem – we actually treat aggressive behavior like this by teaching the dog to associate good things with whatever he’s currently worried about.

      So for example, you might start by giving him a tasty treat each time he sees another dog, or a child. Punishment is not recommended (even relatively “mild” punishment like scolding) because it doesn’t address his underlying discomfort, and can make him even more anxious around dogs and kids over time. Avoiding potential problems by putting him in another room with a special long-lasting chew treat when strangers are visiting, or choosing places to walk where you’re not likely to encounter kids or other dogs, can also be very helpful.

      Ideally, it’s best if you can work with someone in person to teach both of you the skills you need to make things better. Feel free to send me a private message (click the “Contact Me” tab on the menu at the top of the page) and let me know where you’re located, if you like – I’d be happy to try and recommend someone in your area who can help.

  8. I just found your blog — you have some great posts & info! I find the topic of neutering incredibly incredibly confusing, because I think there is a lot of issues that still haven’t been addressed.

    My partner and I have a 9 month old Border Terrier. He is still unneutered. I wanted to wait until he was at least a year to neuter him, but that is proving to be very difficult. He is no longer allowed to go to doggie daycare because of neutered males showing aggression towards him (I have seen him “stand up for himself” and get in a couple of scuffles — no damage to either dog, just scary sounding. I haven’t seen him start a fight and he loves playing with other dogs) and this sometimes occurs when I have taken him to public dog parks. We live in a city where nobody can afford to own their own place and very few rentals allow pets. This means that we only know one other couple who owns a dog. I worry about neutering him because he seems to be going through some fear periods and I’ve heard that the testosterone can help with confidence. But if he is being picked on by other males because he is “different”, then maybe this will eventually cause aggression? Nobody seems to cover the whole unneutered-to-intact dog aggression and how you are supposed to continue to socializing your dog when all your avenues for socializing have been taken away BECAUSE your dog hasn’t been neutered. How much socialization is enough? How many new dogs do they need to meet? Do they have to play together? How much of a role does testosterone play in confidence? So many questions that I can’t seem to find answers to!

    Do you have any thoughts on this?

    1. These are definitely great questions! Unfortunately, as with so many things in the world of dog behavior, we don’t really have black and white answers.

      Regarding whether neutering would be likely to help the situation at doggy daycare – it’s really tough to say without being able to actually observe his interactions with other dogs. I have occasionally seen dogs who seem to dislike intact males more than neutered ones, but this is by no means a universal trait… so if your pup is having recurring issues at daycare with different dogs, I would be suspicious that there may be some other factors in play. There may be something about his play style or general demeanor, for example, that rubs other dogs the wrong way – rather than being just an issue of still having his “boys.”

      So neutering may or may not be helpful, in that respect.

      The good news is, there’s no reason that he NEEDS to continue meeting and interacting with strange dogs for socialization purposes. Some dogs do well in doggy daycare and dog park situations, while others don’t. Nothing wrong with that at all – different strokes for different folks, as they say.

      I agree that you don’t want him to continue being attacked by other dogs, as this will eventually cause some fear/aggression issues on his end – so if this is happening frequently, you may want to consider taking him out of daycare and finding other ways to exercise him instead of going to the dog park. Take him for long walks with lots of time for sniffing and exploring, play fetch with a tennis ball, or sign up for a training class – these are all great ways to get your pup some exercise and mental stimulation without setting him loose in a free-for-all environment with other dogs that might not be good playmates for him.

      I hope that helps a bit! Thanks for bring up these great points, and I’m glad you’re enjoying the blog. <3

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