Neutering: What’s Behaviour Got To Do With It?

The surgical removal of the male and female sexual reproductive organs, primarily the testicles and the ovaries is known as neutering. More specifically neutering male dogs is called castration and spaying when referring to bitches.

Most dog owners’ reach a time when they have to decide whether or not they will have their pet neutered, most vets will recommend this however the age at which they suggest it will vary. There are many health benefits to neutering dog such as eliminating chances of infections such as pyometra and decreasing the risk of getting some cancers. However there is scientific literature which suggests some concerns over neutering such as those discussed in a review by Laura J Sanborn titled “Long-Term Health Risks and Benefits Associated with Spay / Neuter in Dogs” May 2007 which is freely downloadable on the internet.  In this review Laura Sanborn concludes to conclude: “An objective reading of the veterinary medical literature reveals a complex situation with respect to the long-term health risks and benefits associated with spay/neuter in dogs. The evidence shows that spay/neuter

correlates with both positive AND adverse health effects in dogs. It also suggests how much we really do not yet understand about this subject.

On balance, it appears that no compelling case can be made for neutering most male dogs to prevent future health problems, especially immature male dogs. The number of health problems associated with neutering may exceed the associated health benefits in most cases.

For female dogs, the situation is more complex. The number of health benefits associated with spaying may exceed the associated health problems in many (not all) cases. On balance, whether spaying improves the odds of overall good health or degrades them probably depends on the age of the dog and the relative risk of various diseases in the different breeds.

The traditional spay/neuter age of six months as well as the modern practice of pediatric spay/neuter appear to predispose dogs to health risks that could otherwise be avoided by waiting until the dog is physically mature, or perhaps in the case of many male dogs, foregoing it altogether unless medically necessary.

The balance of long-term health risks and benefits of spay/neuter will vary from one dog to the next. Breed, age, and gender are variables that must be taken into consideration in conjunction with non-medical factors for each individual dog. Across-the-board recommendations for all dogs do not appear to be supportable from findings in the veterinary medical literature.”


I am not a veterinary surgeon and am not suggesting that you do, or do not neuter your dogs in relation to any veterinary benefits, however you should discuss whether neutering your dog is the right thing for him/her and when the best time to do this would be for your individual dog. 


Another reason many owners consider neutering their pet is for the perceived behavioural changes. There is popular believe amongst some people that neutering will reduce or eliminate aggressive and ‘hyperactive’ behaviour in dogs. In my experience this is not generally true. Neutering your pet will result in change to your pets behaviour based on the effects of hormonal changes which will occur following the surgery however these are often different to many peoples perception.


Neutering is likely to result in changes to a dogs behaviour, primarily those which are under hormonal (I use this world in this article to mean chemicals produced and regulated by the reproductive systems which are altered by neutering) stimulation such as some types of humping behaviour, some types of escape and roaming behaviours and possibly some types of aggressive behaviour towards other dogs where it is believed the behaviour is hormonally triggered. However these behaviours will also have a conditioned (learned) component to them especially if they have been practiced for some time. Dogs will also show the behaviours listed above for other reasons; I have seen many dogs humping the owner or people within the house where I believe the behaviour is more related to attention seeking rather than triggered by the dogs ‘sexual desires’. Where this is the case neutering your dog is not likely to deal with the reason the behaviour is happening which could be because the dog does not get enough attention for engaging in more desirable behaviours throughout the day but get the most attention when he or she starts to hump. If the humping is believed to be based on a hormonal motivation then neutering will definitely help and sometimes completely eliminate the behaviour, however there are times when training will also need to be done to address the learned behaviour too.


Neutering dogs that show aggressive behaviour is an area where I believe neutering is use too much as a behaviour modification tool. In some situations I believe it is likely to make the aggressive behaviour worse. If a dog is showing aggressive behaviour towards then you should first consult your vet who will rule out possible veterinary causes then if they feel it is behaviourally related they can refer you to a suitably qualified and experienced behaviourist who can assess your dog to see what they would recommend, this may or may not include referring you back to your vet recommending neutering. One of my concerns in neutering a dog showing aggressive behaviour is if that behaviour is based on anxiety or fear (these are the most common reasons for dogs showing aggressive behaviour from the cases I see). I have seen dogs that the owners have described as “getting worse” after neutering and I believe that this could happen as the hormones which would partly provide ‘confidence’ to the dog in these situations are removed so the dog is in a heightened state of anxiety / fear. Where an owner wants to neuter their dog and where the dog already shows aggressive behaviour that I do not feel is driven or influenced negatively by hormones I will work the dog and owner through the problem behavioural areas first before suggesting they neuter.

I also have a similar concern where dogs that show fear related behaviours especially towards other dogs and people being neutered before the dog has learnt appropriate coping strategies and the owner is competent in understating their dogs behaviour and how to support their dog in these situations. A suitably qualified and experienced behaviourist such as a member of the Association of Pet Behaviour Counsellors ( would be able to provide this help.

I believe the age at which a dog is neutered is also important; In the UK vets often suggest dogs are neutered around 6 months and both pre and post season when the dog is a bitch. In many parts of America neutering is happening when dogs are young as 12 weeks old. I personally believe dogs are individuals like people in terms of their psychological and physical development and for this reason I do not believe that all dogs should be neutered at a pre-set age regardless of their behaviour at the time of neutering. I definitely believe that 12 weeks is far too young and there are questions / concerns in the scientific literature regarding bone development in dog neutered this early. Dogs also go through various developmental phases, which include what is popularly known as ‘fear periods’; it is believed that dogs will go through two of these ‘fear periods’ during their development from a puppy to an adult. One will be around 8-14 weeks and other between 6-14 months, the are range is so wide because different dogs will develop and experience these sensitive periods at different times, smaller dogs are likely to mature sooner and bigger dogs much later. If you intend to neuter your dog I would suggest that you base the age on your individual dog and ensure that your dog is not going through a sensitive phase at that time. If in doubt delay! Often owners notice their dogs behaviour change temporarily, the dog may show a ‘bizarre’ hesitation of something they may have previously been fine with or seem more sensitive to the novel sights and sounds. I personally like to wait until my dog is showing signs of physical and behavioural maturity such as cock of his leg if he is a male. With bitches I personally like to wait until she has had at least one season, however this does require some management when she is having her season and she could have the potential to have a false pregnancy. In some cases waiting until after a second season can also be beneficial for her development, again this is my opinion not fact. I believe that bitches should be neutered if you do not intent to breed from them because I feel that the risk assessment is otherwise too high in the favour of her getting an unwanted condition. I do not believe that there will be a negative impact on your bitch’s behaviour in general if neutered at the best time for her. It is not true that it is kinder to allow your bitch to have a litter first before you neuter her, breeding dogs should not be taken lightly as there are too many dogs in rehoming shelters already. In 2011 the Blue Cross saw a 27 per cent increase in stray or abandoned animals visiting them! If you are not going to neuter your bitch or are going to allow her to have a season I would strongly suggest that you keep her away from other dogs until she is fully out of her season or until other dogs stop paying lots of attention to her because I have seen some bitches become less tolerant (even start to growl at, snap at and bite) other dogs after they have experienced lots of invasive sniffing and being pestered just before, during and just as they are coming out of season.

With male dogs I would neuter if they showed increased signs of sexually related behaviour such as humping, roaming, redirected aggressive behaviour which is hormonally driven / influenced or increased frustration resulting from the motivation to engage in sexual behaviour.  However if I have a male dog that does not show these signs then I am likely to keep them entire and only neuter if the need arises. It could be argued that neutering makes it easier to manage the dog in terms of them being less distracted and so more likely to be responsive to the owner; however again in my opinion this is what training classes are for (if you are looking for a training class ask yoru vets for a recommendation or visit the website for the Association of Pet Dog Trainers ( When you have an entire male you do need to be observing interaction with unknown entire male dog when out walking more than your would an interaction with a bitch or neutered male. I also believe that good appropriate socialisation and social skills with other dogs from an early age is crucial if you are going to keep your male dog entire and be meeting lots of other entire male dogs on walks too. If you have an entire male dog who does start to get into fight with other entire males then speak to a behaviourist before it keep happening over and over again until it has a large learned component to it. One of my dogs is entire, I see a difference in his behaviour with other entire males, he is a more tense. Based on Cody’s personality type, predisposition, temperament, socialisation and general learning experiences with other male dogs so far he chooses avoid conflict where as another may get into a fight in the same situation. This may also influence whether you think neutering your dog may be better for him and you than not. Not neutering may mean restricting where you walk and if you live in a low entire male dog density area then this is probably not a problem but if you live in a more highly populated area where there are lots of other entire male dogs you may have to be more selective where you walk and this may mean your dog gets less freedom which for a dog who enjoys free walks this would be a problem.

There is a big move to neuter ‘all’ dogs at a set age. I hope in this article I highlight the two sided though process that should be given when deciding to keep your dog entire or neuter him / her. I believe there is a bigger call for more individualised assessment of dogs, their behaviour, upbringing, sourcing and physical health. This may require an owner, vet and behaviourist working closely together to make the best choice for the dog and his/her environment as a whole.


Although I agree with most of what you stated, in the U.S. shelter dogs by law are required to be neutered or spayed before they are adopted. I was quite shocked that Fenton, my little Dauchsy/Terrier Mix, had to be neutered at 10 weeks before I could take him home. I was concerned about the effects on his develpment, but I cannot complain one bit because as far as this little guy goes, he is one cool little cucumber and healthy as can be. He is extremely social, appropriate during play, loving, well-adjusted, and fun. He is also incredibly easy to read when meeting new dogs. He is one dog savvy little man. I trust him, impllicitly. So, I'm on the fence. I trust my vet to advise me and my clients on this subject, but I am always interested to hear what other well-informed professionals have to say on the subject. Thank you for your very thorough research. It's important to keep up on new research, learn,

and share new things.

In the US, state laws decide whether a dog must be neutered prior to adoption by an adoption group.

In Sweden, my recollection is up to 90% of dogs are not neutered, and they have very few homeless dogs.



The law also thinks the best way to deal with dangerous dogs is to have BSL.


This is an interesting perspective on neutering, one that I have not heard before. In my experience, dog professionals pretty much universally recommend neutering, at least in my part of the country (Ohio). 

Thanks for the info, but please have someone edit your writing before you post. I had to read through several of the paragraphs 3 or 4 times before I understood what you were trying to say. One paragraph starts off saying that "neutering is use[d] too sparingly as a behaviour modification tool" but then goes on to explain how neutering should be used MORE sparingly/less automatically for aggressive/fearful dogs.

I get what you're saying, and I agree, mandatory sterilization sure doesn't make pet owners more responsible, but I don't think that is necessarily the point of it. Context is important. How do you feel about the spay/neuter policy of many (if not most) shelters in North America? The pet overpopulation problem is REALLY BAD here.

I'm not happy that my bitch will be on medication for the rest of her life due to hormone-specific incontinence from being spayed, but if it keeps any one person from being able to accidentally or irresponsibly breed their rescued dog or cat, then I can live with it. I don't think shelters really have the resources to do much more than that in this cultural climate.

I agree with the above comment. The author of the post keeps saying that "neutering will not solve the problem of irresponsible owners." True, but choosing not to neuter won't solve that problem either. Neutering will, however, limit the adverse effects of irresponsible owners who abandon or breed their dogs. 

There is a good point in this post, that there are several reasons for responsible dog owners to consider leaving their dogs intact. The problem is that most dog owners are not going to go through the type of individualized thought process that the author proposes, with a vet and behaviorist.


This topic has gotten very "politicized" because many responsible and legitimate breeders are in total opposition to all laws that they imagine might threaten their rights to continue breeding dogs. They seem to fear that even very well justified laws will be the entering wedge and slippery slope that will lead to total bans on all dog breeding.
This has led to many people seizing on every slight pretext for finding any adverse effects of S/N at any age or at pediatric ages as something that can be used to combat things like higher license fees or S/N laws.

Now recently a lot has been written on this topic. Many of the reviews are biased in one direction or another by the writer's desire to find adverse or beneficial effects. Many mis-interpret or mis-state the meaning of the underlying research. Much of the underlying research is poorly designed (comparing groups that have many other differences other than the one under consideration -- ie comparing apples to tomatos in many cases) or limited to one breed that has a higher than normal incidence of a given problem (eg Rotties re bone cancer) or is limited in meaning by being based on very small numbers of dogs.

There's a review of the literature posted a couple years ago on the UC Davis Shelter Med site by Dr Sheila Segurson.

Meanwhile there are really only a few studies or lines of evidence that would seem unbiased, adequate numbers of dogs, comparing groups that are equivalent other than in respect of S/N status or age of S/N, and so on.
Some years back Guide Dogs of San Rafael began a longitudinal study of effect of age of neutering on their dogs that were intended as Guides (and thus would be followed-up throughout their lives). They had 3 different ages for neuter. The results were a complete absence of any statistically significant difference between the groups with the sole exception that there was a very small increased incidence of conjuntivitis in one group -- a condition easily diagnosed and cured. Now this was published when the dogs were only 2 years old. The intention was to continue following these dogs during the rest of their lives. Similar studies were being done for bitches. So this kind of study will eventually give us very reliable data. At least relevant to these particular breeding lines. Might or might not represent dogs from very different breeds.

The other interesting evidence on results in health of leaving dogs intact comes from the veterinary health insurance companies in Sweden. There at least one half (more recently 3/4) of all dogs have health insurance. So that's a pretty good sampling of the entire population. And the veterinary tradition has been to NOT do S/N for reproduction prevention but to do it only on case by case for health reasons (eg one assumes for pyometria, repro cancers, etc). Well the result has been that the Swedish vets found that over half of older bitches get mammary tumors and over half of older bitches get pyometria. So now they are changing their attitude about doing routein S/N on bitches whose owners don't intend them for breeding. Ie the health advantages for the bitches are now considered overwhelmingly in favor of spaying. I assume they will adopt the evidence from other countries, chiefly USA, that spaying prior to first heat almost totally eliminates risk of mammary cancer, spaying between first and second heat reduces risk, and spaying after second heat has no effect on mammary cancer. Spaying at any age will of course eliminate risk of pyometria and its necessitated emergency spay on a very sick bitch.

True enough that in the Scandanavian countries there are relatively few unintended litters and relatively low incidence of dogs being discarded into the shelters and very high adoption rates for dogs who do land in shelters. That's wonderful of courrse. Why are these countries doing so very much better in these regards than the USA even though a high percentage of dogs are not S/N in Scandanavia ? While many attribute this to cultural differences such that the people there are much more "responsible" than the overall USA population, I don't know if there is any evidence proving that. There would be some other possible contributing factors. The climate could be a factor. In winter perhaps rather few dogs are left outdoors unsupervised, thus haveing opportunity for an unwanted mating ??? Perhaps the strong seasonality might mean that some or many dogs are coming into heat only once a year (wolf pattern) and perhaps only in time to result in a spring litter (wolf pattern) rather than twice a year and just about any time of year (what we think of as domestic dog pattern) ? Or perhaps the leash laws are enforced with great effect on people's behavior or perhaps the people are simply more law abiding ? I don't know what the real reasons might be. If we could discover them, maybe we could change the shelter intake and death rates in the USA.

Now as to behavior of dogs, the earliest published work on effects of neutering males on objectionable behaviors is probably that of Dr Benjamin Hart DVM of UC Davis back over 30 years ago. He found that neutering had substantial preventative and curative effects on some hormone fueled male behaviors. The biggest effect was (not surprisingly) on escapeing and roaming. (No information on how much this affect might be influenced by the level of presence of intact bitches in the neighborhood, ie within wind-born scent distance.) There was also substantial effect on male dog to male dog aggression/fighting. (Today we also are aware that the high testosterone level of a teenager male dog is likely to cause other dogs to start aggression towards him, to "put him in his place" ; I tell people this is like a teenage boy unwittingly wearing gang colors and wandering into some other gang's territory and getting beaten up. ) Some effect on "marking", ie urine marking indoors (no one much cares about outdoors). And some effect on what was considered to be dominence conflicts with owners, aggression to owners. This last item might perhaps get a different description today, as we see fear to be a big factor in a lot of what gets labled aggression to owner and we see owner attempts to forcefully subjugate dogs ("show them who's boss" etc) as likely to result in dog responding with what gets labled as "dominance aggression" to the owner.

We do know for sure that dogs who escape and roam are at risk for death by car, death by other accident, capture by Animal Control and thus risks of not being owner-reclaimed or adopted , thus risk of death by shelter. We do assume as highly likely that dogs who repeatedly escape or who repeatedly fight with other dogs in the home or in public (and dog park) or who can't be convinced not to "mark:" indoors or who are perceived by owner as threatening/aggressive or as dominantly disobedient/untrainable are dogs whose risk of being dumped at a shelter are much higher than dogs without those behaviors. And dogs labled by surrrendering owner as having those behaviors are less likely to be adopted and more likely to be killed in the shelter.

But there is another huge effect of S/N on a dog's behavior and that is the self-fulfilling prophesy effect on the owner's beliefs and expectations and owner's confidence and calmness in dealing with the dog. Now in horses, I long ago observed that a lot of people are afraid of stallions (male horses not neutered) and that stallions get a very "bad press" which exacerbates owner/rider expectations and confidence. I've seen people whose horses improved in behavior immediately after gelding, much sooner than hormone levels could drop. It seemed to me that the "magic act" of gelding gave the owner/handler/rider an immediate boost of confidence and that this change resulted in the change in horse's behavior. Horses are extremely sensitive to the attitude and confidence and skill of the handler. But dogs are even more so.
The same "prophecy" considerations could apply to the effects of telling an adopter the scoring of a puppy or a shelter dog on a temperament test or behavior test. It skews the expectations and the manner the new owner will handle the dog.
We know that a purely bogus statement to teachers that a randomly selected school student (human child) has scored as much brighter tnan average and brighter than current grades would indicate can have the effect of substantially raising that child's later test scores, grades, and opinion of the teacher.

So any research on dog behavior has to take owner beliefs into consideration. Any research on health effects has to take into consideration whether the dog's category has an effect on the kind of care the owner gives to the dog. Eg does a valuable breeding dog get better care than his or her altered littermate sold as a "pet" ? or maybe vice versa ? Does informing an owner that an intact bitch is at higher risk of mammary cancer cause the owner to be more diligent about doing a monthly mammary chain palpation and thus greater chance of discovering a lump if one is present ? or perhaps the spayed pet bitch who loves belly rubs has the better chance of early detection of a lump ?

If it seems like I am raising more questions than answers, that is quite true.

What we do know for sure from shelter stats is that dogs who are not S/N have two to three times the risk of altered dogs that the owner will surrender them. That may be an understatement. go to any shelter and count the ratio of intact males to neutered ones : it's way higher than the ratio in the dogs who are still in their homes. I say males, because with a male What You See Is What You've Got -- well at least for the short coated dogs (harder to see on the shaggy ones). With bitches, you have to look or palpate for a scar and even then it can be hard to tell (especially if she was pediatrically spayed through a minute incision the scar of which is imperceptible).

And we do know for dead sure that those areas that have instituted a universal or near-total policy of pre-release S/N for shelter dogs being adopted will reap the benefits of steady reduction in coming years in their dog intake numbers (or at least intake numbers relative to human population or dog population in the area). So that does mean that pediatric S/N and S/N of all dogs at time of adoption does benefit the overall masses of dogs. The group benefits greatly though it's still possible that some individuals are harmed. so if you agree that "the good of the many outweighs the good of the few" then you have to support shelter S/N regardless of your position on S/N for dogs whose owners claim to be highly responsible .

Are there other things we could or should be doing ? Sure ! We could give free licenses to dogs who are both S/N and have passed the Canine Good Citizen test (very low level on leash test of obedience and behavior) , and give low license fees to those who either are S/N or else CGC, while having very high license fees for the intact dogs who have not passed CGC. that would discriminate against deliberate and accidental breeding by owners too unskilled or lazy to do basic training or with dogs who can't be basic trained (I won't argue how rare truely untrainable dogs might be). AKC could change registration and show rules so that a dog had to pass CGC in order to compete in conformation, maybe also in other performance events, and -- most of all -- that a dog's offspring could not be registered unless the dog had prior to conception date passed CGC.
CGC is a very low standard ; those of you unfamiliar with it, go to the AKC web site and look it up. Those of you used to European dogs who are well behaved in so many public situations are going to laugh yourselves silly at the idea that CGC is even considered a test (rather than what you expect of every dog).

Sorry this post is so long.

I've been doing rescue for my breed throughout N California for the past quarter century. So that's where my bias comes from.

"Every dog's death diminishes me, for I am invoved in dogkind."

The surgical removal of the male and female sexual reproductive organs, primarily the testicles and the ovaries is known as neutering. More specifically neutering male dogs is called castration and spaying when referring to bitches.

HI there; I'd like any info anyone has to this question. We recently altered a dog we had adopted at age about 3 years. Not for any reason except social pressure; we have an excellent situation for him to go when we travel, which is frequently for short periods. For him to have this wonderful second home, nuetering is a requirment, and is broadly accepted here. The effect on my energetic, engaged, spunky little companion is breaking my heart. He is gaining wieght in front of my eyes, in spite of lots of activity and a home-cooked diet of grassfed beef and organic veg; same food we eat. His energy is down-graded and his mood is lack-lustre. I believe that what I am seeing is hormonal depletion and wonder if anyone has any suggestions about getting the balance back. We are very familiar with the effect of hormaonal imbalance in humans--can dogs be that different?

I really loved reading your blog. It was very well authored and easy to understand. Unlike other blogs I have read which are really not that good.Thanks alot!


I have bookmarked your blog, the articles are way better than other similar blogs.. thanks for a great blog!
secret money system review

This is a great post. I like this topic.This site has lots of advantage.I found many interesting things from this site. It helps me in many ways.Thanks for posting this again.
watch movies online

The website is looking bit flashy and it catches the visitors eyes. Design is pretty simple and a good user friendly interface.  venus factor system

thanks for this usefull article, waiting for this article like this again.
Learn More Here

Great info! I recently came across your blog and have been reading along. I thought I would leave my first comment. I don’t know what to say except that I have.
Full Article