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Male dogs, hormones and castration

The topic of castrating male dogs is complicated and everyone seems to have differing views, experiences and beliefs about it. This makes it a minefield of information and often we’re swayed by the advice of vets who we trust to know best for our dogs, but we’ll also be influenced by other dog owners or dog professionals we meet.

Research around castration is fairly limited so we’re often relying more on personal experiences and views, some have seen great benefits from castration while others will have experienced dire consequences.

Ultimately, like everything in the world dogs, the answer to whether or not castration is right for your dog is IT DEPENDS.

If you’re looking for a quick fix for a problem behaviour, castration is very unlikely to magically solve it, so let’s start by saying it is not a solution for behaviour or training issues. It might be one piece of the puzzle and a good thing to do to aid progress, but on its own, it’s not an effective solution.

What the science says about health While scientific research is relatively limited, there have been some studies which give indications of the impacts of castration on health and behaviour of male dogs.

Health wise, castration has been promoted on the basis of reducing the risk of testicular tumours, but it has also been linked to increased joint issues … the science is by no means conclusive but here’s a few findings from various studies:

  • Benign Prostatic Hyperplasia (BPH) is evident in 75% to 80% of intact dogs by age 6, but fixable with neutering. Neutered dogs can still get BPH, but it's less likely

  • Less than 1% of dogs die from testicular tumours and many tumours can be resolved later in life by neutering

  • Undescended testicles make it 13 times more likely your dog will get the most aggressive form of testicular cancer

  • Hip Dysplasia is twice as likely when neutering under 12 months

  • Double incidence of joint disorders when neutering under 6 months

  • Male neutered Labradors are 8 times more likely to suffer with elbow dysplasia

  • 3 times more likely to get bone cancer if neutered before 12 months (especially Rottweilers)

  • Neutering increases risk of prostate cancer, cardiac tumours, mass cell tumours and osteosarcomas (prostate & cardiac tumours are rare however)

  • Neutering increases risk of CCL rupture.

  • Early neutering can cause growth plates to overgrow and increases likelihood of joint disorders

Paediatric neutering

  • Neutering effects on skeletal, physical and behavioural development were the same in dogs neutered at 7 weeks and 7 months

  • Increased evidence of hip dysplasia, noise phobias and sexual behaviours

When it comes to behaviour, again the research is very limited and it’s important to acknowledge that challenging behaviours which appear during adolescence, such as roaming and lack of self-control are often related to adolescent development and as they aren’t sexually motivated, castration is unlikely to have an impact.

Behaviours which are more influenced by hormones, such as mounting/humping, excessive marking, and aggression towards other male dogs, may be reduced after castration but there are no guarantees.

  • Neutering reduced roaming in over 90% of dogs, a reduction in mounting in over 60% of dogs and a reduction in marking for around 50% of dogs (even over the age of 2)

  • Neutering a sexually experienced dog had no impact on reducing mounting

  • Dogs that were neutered between 7–12 months of age, were 26% more likely to demonstrate aggression toward strangers later in life.


Whilst humping/mounting behaviours can be reduced by castrating, there are many reasons why dogs hump, which aren’t always associated with hormones.

There are many different functions of humping and the reasons might surprise you

  • Social bonding / social connection between dogs

  • Scent exchange between dogs: scent exchange aids in recognising family members through scent - they also exchange scent through scent glands in their paws, mouths, base of their tail, backs and shoulders. So this can happen through hip swings, rolling, paws on, mouths on, chin on the other dog and humping!

  • Mounting is an expression of arousal and stress; your dog may hump another dog when they find a situation stressful or exciting.

  • Mounting as a weapon - it may be seen as a low level threat, it nearly always gets a dog into trouble and it’s linked to scent marking and resource guarding (some dogs enjoy the conflict from the trouble, so do it on purpose).

  • Boys can have their sex hat on - you'll see goofy body language; these dogs who hassle other dogs in this way almost always benefit from being castrated.

  • Natures makes sure if it wants a motor pattern to be repeated, it makes it pleasurable

  • Puppies experiment with mounting to see how other dogs respond

  • Neutered dogs can smell like a female so can give off confusing chemical scents

  • No one neuters their brains - they can still be triggered by chemical signals other dogs are giving off.

  • Dogs can hump people- can be attention seeking (very difficult not to give the dog attention for it, so it becomes a jackpot behaviour).

When your male dog is targeted by other male dogs

One area which can be overlooked and many dog owners aren’t prepared for, is the influence of hormones on interactions between dogs. For the sake of this we’ll focus on male-male dogs, but it’s a complex area and females can also be targets of hostility from other dogs due to their scents.

In male dogs, when hormones are changing in adolescence, they can become a target of hostility from other male dogs. Often this will be due to their behaviour, adolescents typically find social interactions highly reinforcing, they may be less aware of signals from other dogs and end up in trouble from hassling dogs, over-sniffing them or behaving inappropriately.

In this case, managing their behaviour more closely and teaching better social skills will avoid negative interactions and ensure everything remains positive.

Where it can become more difficult is if you have an entire male dog who is targeted by others through no fault of their own. Not all of us will have experienced this, but those who have will know how stressful it can be. Have you ever been walking along with your dog, happily minding your own business and out of nowhere another dog approaches and immediately turns on your dog? Perhaps there’s a brief warning as both dogs freeze mid-sniff, or perhaps it’s a straight approach and attack situation. A one-off incident could be brushed off as an encounter with an ‘aggressive dog’, but if it happens repeatedly, it soon becomes an increasing concern for you and your dog.

If you can confidently say your dog isn’t provoking negative interactions (i.e. they aren’t at fault for behaving inappropriately, over-sniffing a dog, barging them around or generally getting in their faces), then reducing the hormonal scents, via castration, should reduce or stop them being targeted by other males. It’s not a guarantee but it’s worth considering if your entire male seems to have a target on his back through no fault of his own.

If a dog has been attacked when entire, they may develop negative associations towards other dogs, they are likely to anticipate hostility and feel fearful, meaning they may act defensively in an attempt to warn dogs away.

Castrating a male who is being targeted, might reduce how often other dogs target them but if they have already learnt to act defensively and fear other dogs, they will also need more training and management to rebuild their confidence. In some cases, the damage is unrepairable.

Castration could reduce their confidence further and worsen reactive behaviours, but on the other hand if it reduces the negative attention they receive from other dogs then it can be beneficial in improving their confidence and skills with dogs. It’s never a straight-forward decision and there are many factors to consider!

Testosterone fuelled behaviours

In adolescence, behaviours which result in internal rewards (i.e. a release of good chemicals and hormones) can be highly addictive. This includes testosterone linked behaviours, for example, risk-taking behaviours can lead to a testosterone boost (risk taking behaviours include running off, ignoring cues, getting into trouble, annoying other dogs, challenging other dogs and winning conflicts)

Some male dogs will find chasing and pinning other dogs highly rewarding, they may also find it addictive to challenge other dogs, especially if they ‘win’ a conflict. Rough play and conflicts with other dogs can quickly become addictive and strongly reinforced in adolescence and lead to an increase in testosterone levels.

Without carefully managing your dog and preventing him practicing these behaviours, they will continue to be reinforced and near impossible to undo later on.

Males who find it particularly reinforcing to target other dogs, win or engage in conflicts, and take risks in social interactions (i.e. really try to provoke reactions from other dogs!) may benefit from castration because it will reduce the reinforcement of testosterone boosts.

However, if behaviours have been learnt and associations have been formed, they may continue to target other entire dogs even after castration, so training and management will still be important and castration alone won’t solve the problems.

Testosterone and confidence

In the past, castration has been promoted as a way to fix aggression, as though it’s a cure for all forms of aggressive or bad behaviour in male dogs. We now know this is far from the truth and there is a risk castration can actually cause more problems than it solves.

"Testosterone doesn't cause aggression- it exaggerates the aggression that's already there"

More often than not, aggressive and reactive behaviours stem from fear or anxiety. These dogs usually aren’t as confident as they may appear and beneath the outward displays, they are struggling to cope. Castrating these dogs before understanding the reasons behind their behaviour is a huge risk.

Testosterone has an important role in confidence, reducing it via castration can have a devastating impact on some dogs.

This is more likely to happen to dogs who are already more fearful or lack confidence, but it’s a risk to all dogs, including those who appear to be relatively stable and confident.

The problem is, we can be guilty of mis-understanding our dogs and assuming their difficult behaviours are due to their hormones or them being too confident. We can so easily miss the signs of fear and anxiety, especially if you have an entire male who is showing reactivity towards other dogs. Even in dogs who don’t have any particularly challenging behaviours, castration can create new issues if it knocks out some of the testosterone that was keeping them stable.

A dog who is genuinely lacking in confidence is rarely a good candidate for neutering. But if your dog has successfully used strategies to 'win' or gain relief, then fear may no longer be the motivating factor.

There is a big difference between a girly young male that lacks confidence, and one that has learned to use aggression as a strategy.

When dogs use aggression as a strategy, it can become addictive. Each time he takes a risk and wins a conflict with another dog, he gets a boost of testosterone which makes him feel great, so he does it again and gets another boost of testosterone. You need to be careful to not let your dog rehearse these behaviours.

Timing, maturity and learnt behaviour

There is a lot to be said for waiting longer before castrating a dog, giving them time to fully mature is likely to lessen any negative impacts. In theory, a more mature dog who has had time to develop fully will be better able to cope with the reduction in testosterone, they will also be out of the turbulent times of adolescence where hormones are ever-changing.

In adolescence, most dogs will experience ‘fear periods’, the timing and intensity of these will vary between dogs, but dogs will be more sensitive during these stages and negative experience can do lasting damage. Castrating a dog during a fear period could be a much higher risk to their confidence overall and leave them with increased fears and anxieties.

For some dogs, castrating at a younger age will be the best option. There are concerns in scientific research that early castration impacts bone development, but for some dogs the behavioural concerns will need to take priority.

Certainly castrating before adolescence is far from ideal, but for individuals who are becoming targeted due to their hormones, castrating earlier in adolescence may be preferable in order to avoid repeated negative experiences.

Castration is even less likely to have any noticeable impact if behaviours have been practiced long-term. Whether that’s scent-marking, hostility towards entire males, or humping, if a dog has spent months or years practicing the behaviour, removing testosterone via castration may make no difference. When a behaviour has been practiced long-term or it has been highly reinforcing, it will be a much stronger habit and require training and management to teach alternative behaviours or undo bad habits. Castration may help in some dogs but it depends hugely on whether hormones are influencing the behaviour or whether the learnt associations are strongest.

Chemical castration

Chemical castration is often considering to be a good option to act as a ‘trial run’, providing similar effects as a full castration but with the benefit of it wearing off.

It's important to understand the affect chemical castration has on your dog's hormones so that you can make an informed decision for your dog:

  1. There is an initial increase in testosterone, which can make testosterone fuelled behaviours worse. If more intense behaviours are rehearsed during this time, they can become permanent. It is important to carefully manage your dog's interactions during the first 4 weeks to ensure unwanted behaviours don't develop and aren't rehearsed

  2. If your dog is negatively impacted by the loss of testosterone, any unwanted behaviours that occur due to the loss of testosterone have many months of being rehearsed before the chemical castration wears off, and this can become permanent, even after the return of testosterone. It's worth speaking to your vet about shorter term options of chemical castration if you decide to go down this route (i.e some vets will do the implant near the groin area rather than the neck so it can be removed rather than waiting for it to wear off).

It is recommended you speak to a professional dog trainer/behaviourist before deciding on chemical castration


There is no doubt that castration is a complicated topic and there’s no right or wrong answer, it all depends on the individual. What’s important is that we don’t jump to the assumption that castration will solve behaviour problems, or equally that castration will ruin a dog. Believing strongly either way can be harmful and it’s important to remain open-minded to the fact that it will depend on each individual dog.

Understanding the emotions and motivations behind behaviours will enable you to make a better judgement on castration and avoids the idea that it will instantly fix problems.

With any behaviour problem, there are many factors to consider and it’s unlikely to be solved quickly, it requires time and commitment and a willingness to understand why the behaviour is happening in the first place.

Castration may well be a beneficial part of improving behaviour, but it won’t resolve anything on its own and it needs to be considered as part of a much bigger picture.

Written by Naomi White

Want to learn more?

If you'd like to learn more about hormones, castrating male dogs and speying female dogs, have a watch of our webinar on 'Should I neuter my dog?' by Mike Newland. In this webinar, he discusses the health and behavioural implications for boths boys and girls.

You can find the webinar for free when you sign up for the Online Academy, along with many webinars on surviving adolescence, socialisation, fear behaviours, reactivity, car chasing, resource guarding, reading body language

If you need support with your dog's behaviour, our residential training stays are a popular training option and are great for:

  • Your dog's training has suddenly regressed now your dog has reached adolescence

  • Your dog has been targeted by other dogs and has developed reactivity issues

  • Your dog targets other dogs and is a bully

  • Your dog is starting to ignore their training to run off to other dogs

  • Your dog has started barking or displaying other unwanted behaviours

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