Everything you wanted to know about castration of dogs.

Posted Monday, 22 May 2017

There is a lot more to this subject than many think. All too often, male dogs are castrated because of the belief that it will calm them down or prevent the development of aggression; however, it is not as simple as that.

Here are some facts about testosterone and how it affects behaviour:

  • Dogs reach the highest levels of testosterone aged approximately 6-12 months after which levels plateau (Pathirana et al., 2012). It is at this time they are most likely to be the target of competitive aggression from other male dogs.
  • Testosterone can increase sexual behaviours (sexually based humping, mating, marking, roaming - looking for a mate).
  • Testosterone can increase confidence (Eisenegger et al., 2016). This is useful for timid dogs but may not be helpful with over confident dogs.
  • Testosterone can be responsible for increased “persistence” (Welker and Carré, 2014).
  • Testosterone can increase risk taking behaviours (Stanton, Liening &Schulthesis, 2011).
  • Testosterone can increase the risk of competitive aggression between males (an adaptive behaviour to ensure the fittest offspring).
  • Testosterone can increase marking behaviours (urinating to mark possessions/territory).
  • Testosterone helps to strengthen ligaments and bone growth as well as support cardiovascular health (Perusquía & Stallone, 2010).

Health benefits of castration:

  • Castration eradicates the risks of testicular cancer (because the testes are removed during castration)
  • Testosterone levels can increase risks of age related prostate issues in later life (Wilson, 2011).

There are some recent studies that concluded other forms of cancer were more likely in castrated dogs. However, since these studies were conducted on animals already suffering from cancers, the sample was biased. There appears to be no evidence that the wider population of castrated dogs suffer from increased risks of bone cancer or mast cell tumours. This sample is already biased as more castrated dogs will suffer from cancers as there are higher numbers of castrated dogs. These studies have been criticised and were not peer reviewed.

What you should know about the effects of castration:

Sometimes, very shortly after castration, some dogs become temporarily manic/reactive. When a male dog is castrated, the testicles are surgically removed under a general anaesthetic. It is the testicles that produce most of the testosterone. As soon as the dog has been castrated, testosterone production stops. However, the pituitary gland appears unaware of this fact and continues to send signals (LHRH – luteinizing hormone releasing hormone and FSH - follicle stimulating hormone) to trigger the testes to produce more testosterone. As the testes are no longer there to do the job, of course, no testosterone gets produced but the pituitary gland continues to produce increasing levels of LHRH and FSH. Eventually, after a week or so, the pituitary gland stops trying to send these chemical messages. In the meantime, LHRH and FSH have been produced in higher quantities than is usual and it is thought this it is these chemicals that can sometimes lead to increased reactivity in the newly castrated dog. It is useful to be aware of this so that you can be more understanding and try to mitigate these behaviours with careful management.

What problems can castration help with?

Castration is usually effective at modifying the following behaviours (as long as the behaviour has not become habitual and as long as the behaviour occurred because of testosterone in the first place)

• Territory marking – urinating to mark territory or resources
• Wandering (if this was caused by mate seeking; however, if not, then castration will most likely make little difference)
• Competitive aggression with other uncastrated male dogs
• Humping behaviours
• It can help prevent your uncastrated male dog from being attacked competitively by other male dogs. This could reduce the risk that your dog could become aggressive to other male dogs later due to learned fear of male dogs.

However, these behaviours are not always modified by castration as they are not always CAUSED by testosterone.

The following behaviours are unlikely to be modified by castration:

  • Any form of fear aggression (castration could make this WORSE by reducing confidence)
  • Timidity (castration could lead to onset of fear aggression by reducing confidence)
  • Unruly behaviour (often this is a simple lack of training, or the result of heavy handed training that leads to frustration and irritability).
  • Wandering due to opportunity/boredom (in other words, not related to mate seeking)
  • Humping due to over excitement or displacement (frustration / stress related)
  • Predatory chase behaviours. 
  • Some dogs mark their area because they are fearful. In this case, castration may not prevent marking behaviours. 
  • Incomplete house training.


The following behaviours can be made worse by castration:

  • Fear aggression
  • Timidity
  • Fear of strangers or strange situations
  • Fear of the vet - (scary operation at vets)

To castrate or not?

If you are having your dog castrated for a behavioural reason, or if your dog is timid/fearful, it is wise to seek the guidance of a qualified behaviourist to help to assess whether castration could help or make the situation worse. If you do decide to go ahead with castration, it is most likely that you will still need to modify this behaviour with the help of a behaviourist as this could have become a learned behaviour. Having the dog castrated would prevent the behaviour being continually maintained by testosterone and can facilitate rehabilitation. 

Chemical Castration

You can assess whether castration could have a detrimental effect on your dog by using a form of chemical castration such as a Suprelorin implant, which mimics castration and is not permanent. However, immediately after implantation, testosterone levels will rise for a few weeks before dropping. If testosterone is responsible for an undesirable behaviour, this increase could see an increase in the problem behaviour. You should discuss with your vet how they can offset this testosterone increase for a few weeks. By four weeks after implantation, the chemical castration mimics full castration. From this time, you can monitor the behaviours to determine if castration would be helpful or detrimental. It is advisable to work with a behaviourist during this time in case difficulties are encountered. The Suprelorin implant should wear off after approximately six months. Obviously, if no adverse behaviours are seen, proceed with castration. 


In conclusion, castration can help to modify some behaviours but is not the answer to all behaviour problems. Without properly assessing a dog, castration could actually make some behaviour problems worse. If you are considering castrating your dog for behavioural reasons, it is best to get assessed by a qualified dog behaviourist. There are health benefits for dogs to be castrated and castration prevents unwanted litters so is the responsible thing to do. If your dog has already mated, castration may not prevent him from mating and tying with a bitch, however, a litter would not be produced from such a tying as long as the dog has not only recently been castrated. Castration can dampen down goading and risk taking behaviours and can reduce persistence so can be helpful in modifying some unwanted behaviours but is not a cure all for all behaviour problems.


Eisenegger, C., Kimsta, R., Naef, M., Gromoll, J., & Heinrichs, M. (2016). Testosterone and androgen receptor gene polymorphism are associated with confidence and competitiveness in men. Hormones and Behaviour doi:10.1016/j.yhbeh.2016.09.011

Emanuele, N.V., Jurgens, J., Paglia, N.L., Williams, D.W. & Kelley, M.R. (1996). The effect of castration on steady state levels of luteinizing hormone releasing hormone (LHRH), mRNA and proLHRH processing: time course study utilizing semi-quantitive reverse transcription/polymerase chain reaction. Journal of Endincronology, 148(3),509-515

Pathirana I.N., Yamasaki, H., N. Kawate et al (2012) Plasma insulin-like peptide 3 and testosterone concentrations in male dogs: changes with age and effects of cryptorchidism. Theriogenology 77(3):550-557

Perusquía M. & Stallone J.N. (2010) Do androgens play a beneficial role in the regulation of vascular tone? Nongenomic vascular effects of testosterone metabolites. Am J Physiol Heart Circ Physiology 298:H1301–H1307

Stanton, S.J., Liening, S.H., & Schultheiss, O.C. (2011). Testosterone is positively associated with risk taking in the Iowa Gambling Task. Hormones and Behaviour, 59(2), 252-256
Welker, K.M., & Carré, J.M. (2014). Individual differences in testosterone predict persistence in men. European Journal of Personality, 29(1), 83-89.

Wilson JD (2011) The critical role of androgens in prostate development. Endocrinol Metab Clin North Am 40(3):577-590