Neutering Male Dogs - the Behavioural Effects of Castration

neutering dogs

Thinking of castrating your dog to solve a behavioural problem? Unfortunately there’s no going back once the deed is done! Before you take the plunge, let’s consider the effects castration may have on your dog’s behaviour.

Castration of male dogs stops the production of the hormone testosterone. This is most likely to be beneficial when treating unwanted behaviours that are more likely in males than in females. Urine marking, roaming away from home to track down bitches in heat, inappropriate sexual behaviour, and inter-male competitive behaviour is often reduced after castration. In contrast, and contrary to popular belief, castration does not “calm a dog down”, since excitable and unruly behaviours are seldom influenced by testosterone.


Testosterone and aggression

Testosterone tends to lower thresholds for aggression (making aggression more likely). It can also make aggression more intense and longer lasting. Thus entire males may be more likely than neutered dogs to respond aggressively in situations where they are feeling threatened or frustrated. Because of the role that testosterone plays in aggression, many dogs behave less aggressively once testosterone levels drop after castration. But the confounding issue here is that testosterone may also act as a confidence boost, and in some cases its absence after castration may mean a dog becomes more brittle emotionally, and more likely to react aggressively when feeling under threat.


Testosterone is often not the whole story

It is also important to note that while testosterone can influence some types of unwanted behaviour, there are normally other factors at play, such as a dog’s environment, prior learning, masculinisation of the brain before birth and during puberty, and the individual emotional and behavioural tendencies of the dog. As a result, even if an unwanted behaviour is influenced by testosterone, castration may not be the easy fix many hope that it will be. For this reason it is critical that the whole picture is taken in to account by a qualified behaviourist, and a behaviour modification programme developed that addresses all the factors contributing to unwanted behaviour.

An APBC-approved summary sheet outlining situations where castration may be beneficial or detrimental for your dog can be found here.  A summary sheet outlining the implications of spaying female dogs can be found here.



Mat has a first class Masters degree in animal behaviour, is a Certificated Clinical Animal Behaviourist, and has trained animals for feature films and commercials.