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Why Is My Dog Aggressive Towards Intact Males?

Adrienne is a certified dog trainer and former veterinarian assistant who partners with some of the best veterinarians worldwide.

Aggression towards intact male dogs.

Aggression towards intact male dogs.

Neutered and Unneutered Male Dogs Together

Some dog owners are puzzled by the fact that their dog is aggressive towards intact males. Often, these are neutered dogs who do well with all other dogs except for those with that little extra detail—they haven't been neutered.

You may wonder how your dog knows whether another dog is intact or neutered. All it takes for us is to ask the owner or bend down and take a quick look under for missing parts. Of course, dogs simply know and don't need to ask or look.

If you think your dog is the only one with this behavior quirk, rest assured that you are not alone. Many dogs, for one reason or another, don't tolerate dogs who haven't been neutered. There are many reasons, and we will look at some below.

Why is my dog aggressive towards intact males?

Why is my dog aggressive towards intact males?

Why Is My Dog Reacting Aggressively Towards Male Dogs?

If your dog reacts aggressively only towards intact male dogs, you may wonder what floats his boat. The causes for this behavior may be several. Let's take a look at some possibilities. However, keep in mind that at times, digging into what may cause certain behaviors is wasted time, and also keep in mind that at times we may never know why Rover reacts in certain ways for sure. Behavior modification for aggressive behavior towards intact males is often the same regardless of the underlying cause.

1. Negative Experiences

It could just be that your dog had a negative experience with an intact male dog and now he is generalizing his bad experience with all intact dogs. It's important to note that your dog doesn't need to have been bitten or growled at for him to develop reactive behavior towards an intact male. Remember that it's about what your dog "perceives as negative" and not what you may perceive as negative.

All it takes at times is something as small as being stared at or an intact dog leaning over your dog for making him feel intimidated and fearful. Remember that a great percentage of what looks like aggressive behavior, in reality, is based on fear.

2. Lack of Socialization

It's very important for puppies to receive a good dose of socialization during that critical window which is open until the pup reaches 12 to 16 weeks of age. During this time the puppy should be exposed to all kinds of dogs of different sex, color, shapes and sizes. The same goes with exposing the pups to people and different environments.

If the dog was never exposed to the scent of a an intact male before, it could likely be that this is something quite new to him and he may react negatively. Some dogs are truly neophobic, which is the term used to depict dogs who are fearful of new things.

3. A Different Scent

Rover won't need to ask the owner if that dog is intact, nor will he have to take a peek under to check for any missing parts. His nose just knows. How? Intact males have a different smell than other dogs.

Indeed, " . . . intact males retain the ability to mate and give off the scent of male, which can be considered a threat to neutered males" explains trainer and behavior consultant Karen Fazio. The hormone testosterone is what gives a dog his "maleness" scent. Interestingly, when dogs reach 10 months, there's a peak in this smell as testosterone levels in the adolescent male dog may be five to seven times greater than the levels of an adult!

This "male" scent may cause neutered dogs to react negatively towards them causing tension and even aggressive displays. When an intact male enters a dog park, you can almost feel the tension in the air. There is the belief that neutered dogs, on the other hand, seem to smell quite similar to females, yet it would be interesting to know if there's any actual proof of this. How can we know if we can't ask dogs?

Doesn't Neutering Reduce Aggression?

Something else to consider is what statistics have to say about neutered dogs. According to two different studies (see references under Reference section), it was found that, contrary to popular belief, spaying and neutering dogs may actually cause an increase in canine aggression. So it could be that neutered dogs may just simply be more reactive towards unfamiliar dogs.

Force-free methods can help change your dog's emotions.

Force-free methods can help change your dog's emotions.

How Can I Help My Neutered Dog?

With many shelters and vets advocating the spaying and neutering of dogs, exposure to intact male dogs should be limited. Also, intact dogs are often not accepted in dog parks. Could this have caused an increase in reactivity to these fellows because they are rare? Could it be that because it's so different it immediately raises a red flag?

Interestingly, there are many countries where neutering is not as in vogue as it is in the US. If your dog is reactive towards intact dogs, and exposure to intact dogs is a common occurrence, you may wonder how you can help your dog. Following are some steps:

1. Seek the Advice of a Professional

The best approach would be to consult with a dog professional such as a certified applied animal behaviorist or a board-certified veterinary behaviorist. These are the experts in the field. Yet, some reputable trainers are well-versed in dealing with dog behavior problems. You can for a trainer using force-free behavior modification methods on the Pet Professional Guild website.

2. Manage Your Dog

The more your dog is allowed to rehearse aggressive behaviors towards intact dogs, the more this behavior will become ingrained and will put roots. Managing your dog will keep him and others safe, and will prevent the rehearsal of unwanted behavior.

3. Use Force-Free Methods

If you hire a professional he/she will show you some effective methods to help your dog deal with his emotions. Great force-free methods are desensitization and counterconditioning. Other possible used methods based on classical conditioning and counterconditioning involve open bar/closed bar, Look at That, and COR training. Operant conditioning by teaching alternate, incompatible behaviors with acting reactive may also later be added into the mix. Always work under your dog's threshold levels.


  • McGreevy PD, Wilson B, Starling MJ, Serpell JA (2018) Behavioural risks in male dogs with minimal lifetime exposure to gonadal hormones may complicate population-control benefits of desexing. PLoS ONE 13(5): e0196284.
  • Deborah L. Duffy and James A. Serpell (2006, November). Non-reproductive effects of spaying and neutering on behavior in dogs. Proceedings of the Third International Symposium on Non-Surgical Contraceptive Methods for Pet Population Control. Alexandria, Virginia.

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

© 2013 Adrienne Farricelli


Val Beasley on November 16, 2019:

This is happening with our neutered rescue male dog...he’s sooo friendly and calm until he meets an intact male....he turns into a different dog! We have learnt to manage this by looking ahead and making sure before he meets any male dogs...what I wanted to point out though...was this exact phenomenon happens with horses too...I used to have horses and worked in a stables...if we introduced a stallion into a field or paddock...we knew he was in danger of getting kicked about...the other males hated’s such a shame...I’m afraid that if someone chooses to keep their male dog unneutered ( which is their right and of no business of anyone else of course) then, I’m afraid that nature sometimes will take its course and aggression will be shown towards them’s just nature, and with the best will in the world, cannot always be totally prevented, even when, like us, we do try our best to keep our dog on a lead away from them, you just cannot fight nature, and so owners of unneutered males must expect some problems occasionally. I wish it wasn’t so, but it’s the animal world, not the human world....

Jmochil on September 15, 2018:

I appreciate this. My 80lb neutered dog is very aggressive to intact males over 6 months of any size. I’m well aware of the issue and am very cautious and am always on high alert fr the rare intact dog that may enter into the dog park. However, more dogs are remaining intact in NYC up to a year. Which is fine but I also think that in a city Enclosed in tight spaces there needs

To be more education about why dogs are aggressive towards intact dogs. Whenever I explain this to owners they are put off (I’ve only had a few,

Who are actually regulars at the park everyday show understanding). Just as much as it is my responsibility to know my dogs behaviors, they should be informed on why it’s happening and the implications. Maybe vets, breeders (not likely to do this) and shelters can help educate new dog owners on the possibility so they aren’t shocked when they enter a dog park and all of a side a pack of dogs stalk and act aggressive towards their dogs. I especially think vets and bleeders at the front line of making recommendations can share this information My new response to these people is that they should ask their vet and I do apologize and take my dog out.

CoCo on December 20, 2017:

My dog who is neutered since a pup, a lab mix is aggressive toward my daughter's intact one year old weinerramer and they got into a fight briefly. I suggested since we're going to be living under the same roof that we should sit down and have leashes on both and reintroduce them talk them saying that is your friend and no fighting. I have trained my dog to not fight or growl at our household cats whether they be mine or my daughter's and there's no problem there. My daughter insists that I have not trained my dog and doesn't want to sit down with them to train them to accept each other. My dog is ten usually gets along with other dogs. I don't know what to do. Thanks

Adrienne Farricelli (author) on September 25, 2017:

Naddy, it means preventing rehearsal of the problem behavior. For example, keeping the dog on leash, walking at a distance from the trigger, avoiding the triggers until you can implement behavior modification.

Naddy on September 21, 2017:

When you say "manage your dog", what exactly does that mean? Thanks.

michael on July 26, 2017:

Dog envy !

Adrienne Farricelli (author) on April 10, 2017:

Hello Melanie and Brian,

Are you looking for other ways to deal with the problem (on top of the ones suggested) or other potential causes for the behavior? If your dog is reactive towards intact male dogs, it's not the intact male dog's fault, but nor is it your fault. These things happen. The problems is that dog parks are not the best place to let dogs socialize, because of problems as such. It is far better and safer to organize play dates with dogs that dogs are known to get along. This prevents rehearsal of problem behaviors while increasing safety. Kudos for you for being able to re-direct your boy before things escalated!

melanieandbrian on April 10, 2017:

I volunteer with dogs in a Shelter for 7 years, having dogs all my life. I have learned a lot, and know that I still have a lot to learn. I was curious the last couple of times at our large dog park when my very agreeable Neutered Pit mix became aggressive with a couple intact males. The aggressive behavior was on my dog, not on the other males part. I did not let him escalate, redirecting him in another direction and activity. By the way, the owner was very nice and told me that this does happen usually in spring and winter. Any other behavior suggestions? Not my job to encourage everyone to neuter their dogs.

Adrienne Farricelli (author) on September 04, 2013:

Epbooks,that's quite an interesting experience to witness!

Elizabeth Parker from Las Vegas, NV on September 04, 2013:

Great hub. I remember volunteering at dog adoptions one day when a new "intact" male lab came to join the group before his surgery, and all of the other male neutered dogs acted like they hated him. Two weeks later, he came back, now neutered and each dog acted like they were the best of friends with him. I never forgot that because it was such a lesson for me. I love the way you explain it here. Thanks!!

Adrienne Farricelli (author) on September 02, 2013:

I think it's awesome for you to be eager to learn as much about dogs. I wished all letter carriers were so interested in canine behavior, I am sure they would all benefit from it, thanks for stopping by!

Mel Carriere from Snowbound and down in Northern Colorado on September 02, 2013:

Your expertise on the subject of dogs astounds me. As a letter carrier I feel that it is part of my job to study the canine mind, and your hubs have helped me. I'm going to be on the lookout for this behavior.