Male Dog Behaviour After Neutering: The Science

Recently, a well-respected Sydney academic published his behavioural data on over 6000 castrated male dogs. It’s created headlines like”Neutering Causes Behavior Problems In Male Dogs”.

Can this be true? You’ve probably been told that desexing reduces behaviour problems, not causes them!

Does Desexing Lead To Aggression?

The reality is, there’s been a debate about this for some time and no-one can agree. But we need to get it right.

  • We’re talking about human-directed aggression
  • Many of those people are children
  • When children get injured, it’s often badly
  • These dogs often get euthanased

Personally, I think the study in question is flawed. It uses a voluntary online survey that was distributed to breeder groups. That’s hardly likely to give a reliable snapshot of the dog population. It also doesn’t have a ‘control’ population of entire dogs.

But to be fair, no study is perfect. The answer is to not look at just one, but consider them all. To try to answer the question, that’s what I’ve done here.

Studies On Aggression & Neutering

Below is a summary of every study I can find that compares aggression towards people between entire and desexed dogs. If it looks a mess now, it’ll hopefully make sense once I explain it afterwards (yes, I read every paper).

check mark= desexed dogs are better
cross mark= desexed dogs are worse
question symbol= no difference detected
StudyPopulationSignificant Findings
Borchelt 1983258 USA dogs diagnosed with aggressionNo difference detectedquestion symbol
Wright et al 198762 dogs referred for aggression problemsSexually intact dogs were more likely to be aggressivecheck mark
Gershman et al 1994178 biting vs 178 randomly selected USA dogsSexually intact dogs were more likely to bitecheck mark
Podberscek et al 1997a217 low vs 218 aggressive USA English Cocker SpanielsMore neutered dogs were in the ‘high’ aggression groupcross mark
Podberscek et al 1997b1019 randomly selected USA English Cocker SpanielsNo difference detectedquestion symbol
Guy et al 20013226 dogs attending Canadian veterinary clinicsAggressive behaviour more common in castrated dogscross mark
Reisner et al 20051053 randomly selected USA English Springer SpanielsNeutered males were more likely to bitecross mark
van den Berg et al 2005110 aggressive USA Golden retrievers vs 118 relativesCastrated dogs were more common in the aggressive group*cross mark
Messam et al 20071112 dogs attending vets in Kingston, JamaicaSexually intact dogs were more likely to bitecheck mark
Hsu & Sun 2010852 randomly selected dogs in TaiwanNeutered dogs scored lower on owner-directed aggressioncheck mark
Casey et al 2014946 neutered vs 855 entire male UK dogsNo difference detectedquestion symbol
Shuler et al 2014636 dog bites reports from 47,526 registered USA dogsSexually intact males were more likely to bitecheck mark
McGreevy et al 20186235 neutered dogs recruited by online USA surveyStranger-directed aggression increased with lower hormonal exposurecross mark

Confused? You’re not alone. Here are my thoughts and impressions:

Studies on single breeds are of limited use. Golden Retrievers are such placid dogs that their aggression is likely to be of a different nature. Aggression in Springers is suspected to be genetic in origin, especially in the show lines.  I place little relevance on these papers, so bear with me while I remove them…

As aggression gets more serious, results are clearer. Of the remaining studies, let’s look only at the dogs being treated for aggression or reported for dog bite to people. Now it looks like this:

StudyPopulationSignificant* Findings
Borchelt 1983258 USA dogs diagnosed with aggressionNo difference detectedquestion symbol
Wright et al 198762 dogs referred for aggression problemsSexually intact dogs were more likely to be aggressivecheck mark
Gershman et al 1994178 biting vs 178 randomly selected USA dogsSexually intact dogs were more likely to bitecheck mark
Shuler et al 2014636 dog bites reports from 47,526 registered USA dogsSexually intact males were more likely to bitecheck mark

Whether you agree or not I hope you can see the reasoning. Random surveys of dogs are going to give different results to studies looking at acts of aggression. But I haven’t quite finished with the confusion.

A reason that entire males might be unfairly blamed is that poorer quality dog owners may also be less likely to desex their dogs. That means that some of the aggression might just be because the owner is an idiot and has raised the dog badly.

A reason that desexed males might be unfairly blamed is that when behaviour problems in males develop, most vets will recommend desexing. That will push more aggressive dogs into the ‘neutered’ groups. This is suspected to have happened in the Golden Retriever study.

Which Males Become Aggressive?

In conclusion, the ‘truth’ will probably be that desexing is good for some types of aggression but worse for others. I suspect it slightly increases the incidence of fear aggression (which often goes unreported) and reduces the more dangerous forms of human-directed aggression.

A clue to this is the dog bite statistics again. When we go one step further and look at fatal dog bites, the majority are children and they mostly involve undesexed males (Sacks).

One of my current concerns regards the delaying of desexing until over 12 months in large breeds. Let me be clear: I support it. However I have seen two lovely Rottweilers become dangerous during the waiting period, and they are likely to stay that way.

There’s no point worrying about a 5% risk of joint problems when you end up with a far worse problem. I advised the delay but I also believe these two dogs should have been desexed as soon as their behaviour started changing. Their futures are now bleak.

I don’t expect to sway anyone’s opinion, and I don’t even want to. All I want is to get the idea across that this debate is a lot more complicated than it looks. It’s full of people with vested interests on both sides only quoting the studies that agree with them.

You are welcome to argue!

Further Reading

You might also like: Reasons for not desexing male dogs | The best age to desex dogs | Why desexing before 6 months can be harmful

*Significant meant the measured difference between the groups had a p-value of <0.05. It’s how we (somewhat arbitrarily) decide if a result is real or not. To learn more, read our guide to making sense of scientific research.

I can supply copies of the references (below) on request. If you know of any other studies that compare aggression in neutered and entire male dogs, please let me know!

Have something to add? Comments are welcome below and will appear within 24 hours of lodging.

By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These blogs are from a series regularly posted on Facebook and Twitter. Subscribe via email here to never miss a story!

Borchelt, P. L. (1983). Aggressive behavior of dogs kept as companion animals: classification and influence of sex, reproductive status and breed. Applied Animal Ethology, 10(1), 45-61.

Casey, R. A., Loftus, B., Bolster, C., Richards, G. J., & Blackwell, E. J. (2014). Human directed aggression in domestic dogs (Canis familiaris): Occurrence in different contexts and risk factors. Applied Animal Behaviour Science, 152, 52-63.

Gershman, K. A., Sacks, J. J., & Wright, J. C. (1994). Which dogs bite? A case-control study of risk factors. Pediatrics, 93(6), 913-917.

Guy, N. C., Luescher, U. A., Dohoo, S. E., Spangler, E., Miller, J. B., Dohoo, I. R., & Bate, L. A. (2001). Demographic and aggressive characteristics of dogs in a general veterinary caseload. Applied Animal Behaviour Science, 74(1), 15-28.

Hsu, Y., & Sun, L. (2010). Factors associated with aggressive responses in pet dogs. Applied Animal Behaviour Science, 123(3-4), 108-123.

McGreevy, P. D., Wilson, B., Starling, M. J., & Serpell, J. A. (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.

Messam, L. L. M., Kass, P. H., Chomel, B. B., & Hart, L. A. (2008). The human–canine environment: a risk factor for non-play bites?. The Veterinary Journal, 177(2), 205-215.

Podberscek, A. L., & Serpell, J. A. (1996). The English Cocker Spaniel: preliminary findings on aggressive behaviour. Applied Animal Behaviour Science, 47(1), 75-89.

Podberscek, A. L., & Serpell, J. A. (1997). Environmental influences on the expression of aggressive behaviour in English Cocker Spaniels. Applied Animal Behaviour Science, 52(3-4), 215-227.

Sacks, J. J., Lockwood, R., Hornreicht, J., & Sattin, R. W. (1996). Fatal dog attacks, 1989-1994. Pediatrics, 97(6), 891-895.

Shuler, C. M., DeBess, E. E., Lapidus, J. A., & Hedberg, K. (2008). Canine and human factors related to dog bite injuries. Journal of the American Veterinary Medical Association, 232(4), 542-546.

Van den Berg, L., Schilder, M. B. H., De Vries, H., Leegwater, P. A. J., & Van Oost, B. A. (2006). Phenotyping of aggressive behavior in golden retriever dogs with a questionnaire. Behavior genetics, 36(6), 882-902.

Wright, J. C., & Nesselrote, M. S. (1987). Classification of behavior problems in dogs: distributions of age, breed, sex and reproductive status. Applied Animal Behaviour Science, 19(1-2), 169-178.


5 Replies to “Male Dog Behaviour After Neutering: The Science”

  1. How refreshing! A piece that actually rationally presents the multifaceted desexing issue and looks at all the potential influencing factors on data.
    This is the first non-biased, logical article I’ve read on the subject. Thank you!!

    I have a 9 month old (70kg) Great Dane and my vet has been pushing so hard for me to have him desexed. I have to argue every time that I want to wait until at least 12 months for joint issues and to reduce the chances of osteosarcoma as much as possible. I made the mistake of telling him that my puppy occasionally shows fear based responses to tall male strangers (backing away, tail between legs and ‘boofing’ noises). I’m using clicker training and rewards to try to counter condition him and it’s working well. However, my vet is convinced this is aggression and has told me I’m “irresponsible” for not having him desexed yet. I’ve read the studies and am under the impression that castration may worsen fear based aggression but he strongly disagrees.

  2. Not just responding to this article, but your entire blog; everytime I read something here I am better informed as a pet companion. Your informative and neutral style is a rarity in this internet age. Thank you for sharing your study, knowledge and experience.

  3. Good to see a rational approach and voice when it comes to attempting to make sense of the studies.
    Like so much in the medical world, things are rarely simple…..example skin allergies are not necessarily related to the food eaten – allergies are so much more complex, even if there is a genuine food allergy, it is often much more complex than an allergy to protein – which most people think of as meat but there are proteins within proteins

    Likewise, Behavioural problems are so much more complex than age of desexing or if someone mistreated an animal at some stage in its life (usually a bearded man with glasses, wearing a baseball cap and maybe a high Vis vest whilst holding an umbrella)………we now know behaviour can start with the parents of an animal and how they themselves have been treated or maybe had an illness during pregnancy.

    The fact is you have raised some valid points on the validity of the data – it would be very interesting if the questions you ask would ever get taking into account with the data collected.

    People will enviably believe what they wish to believe – but in all I think this is a very considered and reasoned piece on the debate

    1. Thanks Gillian. Dr Paul McGreevy has authored some great studies and I certainly don’t want to detract from his work. It’s more an example of the need to identify the limitations of any research. I hope one day to ask him directly about this one!

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