Muddy Mutleys

Dog Training & Behaviour Specialists

Testosterone and Aggression. Castration is the Silver Bullet?

Testosterone is a hormone much talked about in relation to dogs and dog behaviour and key in the decisions that many make about whether to neuter their dog or not.

I thought it would be useful to share some information on testosterone and the role it plays in relation to aggressive behaviour so that you can make a more informed decision in conjunction with the advice of your vet. 

Firstly, it is important to understand that removing testosterone through neutering your dog, may, in some cases depending on the function and motivation of the behaviour and depending on the overall nature and personality of your dog, decrease aggressive tendencies, BUT IT WILL NOT eliminate aggression. 

If in a very unethical experiment, testosterone levels were increased to an exaggerated extent, you might see an increase in aggression but increases and decreases within normal or natural levels will not have an impact one way or another on offensive or defensive aggressive behaviour.  In fact, with the more fearful dogs, neutering can in fact make things worse.

Interestingly behaviour drives hormonal changes rather than hormones driving behaviour. Displays of aggression elevate testosterone secretion.  However, levels of testosterone don’t predict who is going to be aggressive. Testosterone doesn’t cause aggression; it enhances it in those that are already aggressive.  Hormones rarely act outside of the context of the environment they are in.

Let’s look at the fight of flight system, the sympathetic nervous system that gets the body ready to either run away from a threat or to fight for our lives.  During an aggressive altercation, part of the brain, the amygdala, communicates with the hypothalamus sending bursts of action potentials; activating the nervous system, pumping blood to muscles, getting the animal physically and physiologically ready to fight in the context of aggression.  

Testosterone doesn’t cause this to happen, but if this is already happening, testosterone will increase the rate of these action potentials by shortening the rest time between them.  In other words, testosterone is not responsible for turning the tap on, but it will increase the flow. It’s not causing aggression its exaggerating a pre-existing pattern and exaggerating the response to environmental triggers.

Social conditioning makes up for the hormone, so removing testosterone will not necessarily remove the propensity for aggression.  Learning history will determine the behaviour, the behaviour will determine the levels of testosterone. There is research to support that testosterone intrinsically reinforces aggressive behaviour.  Those that win have a surge of testosterone promoting a feeling of wellbeing and elation at victory, making the behaviour much more likely in future. 

As testosterone appears to facilitate aggressive arousal and aids the dog in preparing for agonistic success, it is important that we learn to spot and learn reliable methods of interrupting a direct stare at a potential target as quickly as possible. Testosterone enhances selective attention towards a target whilst acting as a block towards other external stimuli. Therefore, once attention is frozen on a target it is very difficult to redirect the dog onto something else. Reduction of testosterone through castration may make management of this situation easier.

Castration may result in a drop in male sexually dimorphic behaviours such as intermale aggression (but not offensive or defensive aggression), urine marking, roaming, and mounting Neilsen et al 1997 reduction in behaviour 50% – 90%

Let’s look at humans, who we don’t castrate, for a second with the help of Robert Sapolsky and his book, “The Trouble with Testosterone”.  Although studies link high levels of testosterone to aggression, this hormone alone does not account for aggressive behavior. In fact, successful athletes and businessmen tend to have high testosterone levels, without being any more violence-prone than their low testosterone counterparts, indicating that testosterone may not act alone in promoting aggression. Rather, aggressive men’s behavior may be influenced by high testosterone levels combined with low levels of the brain chemical serotonin.

Going back to the hypothalamus and the amygdala mentioned earlier, both these parts of the brain are prominently associated with both testosterone and serotonin, both play a key role in aggressive responses towards a target. In comparison to nonaggressive animals, aggressive animals have been found to have lower serotonin levels in the hypothalamus and the amygdala.

So, rather than testosterone being key, perhaps then more important is ensuring that our dogs are on the best possible diet to ensure good gut health, where more than 95% of serotonin is produced.

To summarise, it’s useful to use the words of Dr Karen Overall who explains that testosterone acts as a behaviour modulator.  Exposed dogs who have inappropriate behaviour pattens may be more reactive and may react to a stimulus more quickly. They may react more intensely and may react for a longer period of time and take longer to recover. (Overall K 2013)

Although castration might provide an edge by decreasing the chemical impetus towards reactivity, it does nothing to diminish the learned component.  And this is where good training and, environmental management with a good Behaviour Practitioner, can really help you to make a difference.