Do dogs become more aggressive after neutering

This is a really interesting question, and raises a number of really valid points. To answer it, we need to look in more detail the reasons why dogs behave the way they do, and the hormonal influences on them.

Common misconceptions of neutering

It is widely – and falsely – believed that neutering “calms a dog down”. However, an adult or adolescent dog’s basic temperament is relatively independent of testosterone, and neutering won’t make any significant changes to his intelligence or personality. What it can do is affect his emotional state, and what behavioural options occur to him.

So what does testosterone do?

In behavioural terms, testosterone has two main functions.

Firstly, it is the main trigger for a dog’s sex drive – so any behaviour driven by the need to breed will be at least partly influenced by testosterone levels. This would include roaming in search of bitches in heat, humping and masturbation (although see below!), and, interestingly, urine marking. All of these behaviours are reduced (if not eliminated) by castration.

The second is that testosterone does appear to increase the expression of aggressive behaviour. This might be an evolutionary hang-over from having to fight for mates, but whatever the reason, the threshold for initiating an aggressive act becomes lower the higher the dog’s testosterone level is.

So, an entire dog is more likely to respond to annoyance or frustration by snapping than a neutered one is. The exact mechanism isn’t clear, but testosterone is also a major factor in determining a dog’s levels of self-confidence, so he may be more likely to start a fight because he’s more likely to believe that he can win it!

What does testosterone not do?

It doesn’t initiate any particular behaviour, it just alters the likelihood of that behaviour being expressed. For example, not all “sexual” behaviours are actually linked to sex drive – so humping and mounting can occur in neutered animals as well. These patterns of behaviour are “hard-wired” into a dog, but they can be used to express different things – for example, mounting may be an expression of dominance. Some neutered dogs also continue to hump, possibly because it has become a learned behaviour.

As far as we can tell, testosterone is also NOT involved in the vast majority of “unruly” or “disobedient” behaviours. While adolescent dogs are more easily distracted, and are full of energy, poor behaviour at this age is more often related to poor training.

So, shouldn’t castrating make him less aggressive?

Unfortunately not necessarily, and for a very simple reason…

There’s more than one type of aggression!

Aggression between male dogs is mediated largely by testosterone; however, aggression towards people, female dogs and other animals is far more weakly linked to his hormones. If you think about it, it makes sense: if you’ve got to fight other males to get access to a mate, there’s no point in fighting against the females, or against other species who aren’t competing with you.

Aggression that is directed towards people, other animals, or generalised (anything that moves and looks suspicious) is most likely to be fear-based aggression. And unfortunately, fear-based aggression is often made WORSE (or even triggered) by castration. While it would be a nice story to say that dogs became anxious after castration because of the psychological trauma from the loss of their testicles, this doesn’t actually happen. What does happen is a fairly rapid drop in blood testosterone, the very hormone that was keeping them self-confident and relaxed in the presence of potentially threatening objects. So, we might well imagine that the dog’s thought process of “yes, that person’s a bit scary, but I’m sure I could take them so I don’t need to worry” changes to “oh no, that person’s scary, I need to drive them off before they can hurt me”. Without that confidence-boosting hormone, dogs who are prone to anxiety often get a lot worse.

So can we replace the testosterone?

In theory, yes. However, there aren’t any licensed products in the UK, and you could be storing up problems for yourself. As we’ve seen, testosterone has complex and subtle effects on the brain, it isn’t anything like as straightforward as many people think (and it still isn’t fully understood).

Many male animals are neutered (castrated) as a best practice for health and handling. Castration is often considered part of responsible pet ownership. Much research has been done about the health and behavioral impacts of castration in pet dogs.

Pet overpopulation is a global concern and unplanned litters account for a staggering number of euthanasias in the United States and around the world. Preventing unplanned litters is a crucial part of responsible pet ownership. Castration is one way to prevent unplanned litters, although the timing of this procedure has come under more scrutiny within the veterinary science community in recent years.

What is involved in neutering a dog?

Neutering, or castration, is the surgical removal of the testicles. Removing the testicles removes the primary source of testosterone in the body, resulting in changes in sex drive, hormone-related behaviors, and hormone-related health concerns. Removing the testicles can also protect against some later-life health concerns, such as testicular cancer and prostate enlargement, as well as hormone-related tumors of the perineum. Neutering may also be associated with an increased risk of some musculoskeletal disorders and cancers, when done before a given age.

When should my dog be neutered?

All dogs are not physiologically the same. Different breeds and sizes of dogs have different optimal ages for castration. According to a recent study, veterinarians and pet owners should work together to discuss the optimal age of neutering, instead of following a blanket age recommendation. Every dog owner should consult with their veterinarian about the health impacts of castration for their individual dog.

Historically, veterinarians have recommended neutering dogs before puberty. This not only minimizes the risk of unplanned litters, but also may offer behavioral benefits. Puberty and adolescence are the time when animals transition from youth to sexual maturity. In most breeds and sizes of dog, this period spans from 6 months to 2 years of age. Hormone surges during puberty can and do influence the behavior of any individual. Ask the parent of any teenager! If you’re considering waiting until social or structural maturity before neutering, be sure to talk to your veterinarian in-depth about what to expect with respect to your dog’s needs for exercise, training, appropriate and safe confinement, and appropriate social environments.

What are the impacts of neutering on dog behavior?

The best predictors of a dog’s behavior are his genetic background combined with the social learning and training he receives. Reproductive status does play a role in behavior, but it is not the dominant influence over animal behavior.

Testosterone influences sex drive and sexual acts, searching for mates, territorial behavior such as urine marking, and aggression between males. Testosterone may also affect confidence and the role of the experience of fear in some dogs. Neutering will result in a reduction in sexual behaviors (breeding attempts and masturbation), seeking mating opportunities, and urine marking. Some of these sexual behaviors can be dangerous, resulting in fights between dogs, roaming and being injured by cars, fences, poisons, and other threats, and neutering will decrease these risks.

There is conflicting evidence at this time, but it is possible that neutering males before puberty may correlate with increased aggression directed toward strangers and strange dogs. However, further research is needed before any firm conclusions can be drawn in this situation. Neutering was historically considered a crucial part of therapy for all dogs displaying unwanted aggression. A more careful examination of the aggression with a veterinarian experienced in treating behavior disorders is now recommended prior to neutering, as neutering may worsen fear-related behaviors in a small subset of dogs.

Is there an alternative to neutering my dog?

Dogs can also be sterilized using vasectomy. In dogs for which castration at any age may be associated with adverse health risks, vasectomy is an excellent alternative to prevent unplanned litters and continue to control the pet overpopulation epidemic.

Do male dogs change after being neutered?

How long are dogs aggressive after neutering?

Why is my dog acting crazy after being neutered?

Does neutering affect dog temperament?