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A Note on Neutering, Spaying and Chemical Castration

As a certified dog trainer and an admin for a professional pet care group, I am often asked, what is my opinion? The truth is I don't have an opinion and cannot offer any anecdotal advice. Why? Most importantly, because I am not a veterinary professional or scientist. Only a vet can offer or give advice in regard to an animal's health legally under the Vet Act and due to liability. So I am sharing collected information from veterinary and scientific sources in relation to behaviour.

There is a lot of research that shows particularly early neutering and spaying is related to many physical and likewise behavioural problems. Following neutering, decreases in hormones in some dogs may cause a negative effect or change in behaviour and could need immediate veterinary and behaviour support. Your personal or client's vet will hopefully refer to a clinical behaviourist. This is why many vets recommend chemical castration as not permanent.

The hypothalamic–pituitary–gonadal (HPG) axis is essential for homeostatic balance of reproductive functioning. Sex-related hormones and receptors are seen throughout the brain’s limbic system, functioning as neuromodulators and neurotransmitters, affecting sociosexual behaviour and emotion (Carter, 1998). The hormones are required for healthy brain function and behaviour. Elevated levels of testosterone correlate with higher levels of confidence and resilience (Eisenegger et al., 2017; Cherki et al., 2021). Meaning, that these hormones are required to regulate behaviour and having a confident dog.

This is one more recent paper, reviewing research and breeds in relation to this subject.

"Neutered dogs are more likely to become more anxious and insecure." (2017)

Most vets are up to date with research and not advising dogs are neutered until physically fully developed. And will not advise neutering or spaying dogs that show fearful or anxious behaviour. There is also no evidence that unneutered and unspayed dogs are more destructive behaviour wise.

This is based on scientific research, what is best for a dogs welfare physically and behaviourally. This is something that dog professionals and rescues need to be up to date with, as many dogs end up in rescue, based on physical conditions and behavioural problems.

And why a rescue will have a contract, including neuter, spay to be carried out under vet advice. Vet advice has changed during recent years based on current scientific research showing early neutering or spay has negative effects.

Serpell through research has also found that neutered dogs have difficulties with ongoing learning (Serpell et al, 2005). This is something to be aware of in regard to animal welfare and in terms of ongoing training and learning.

In a 2021 study review the researchers stated that there was a common belief that castration reduces aggression, but there is an absence of agreement in all literature.

"Clearly, gonadectomy does not result in a predictable decrease in aggressive behavior across all male and female dogs."

Also noted in the above 2021 study was an extensive review of the related literature conducted in 2010 that concluded that the data collected does not demonstrate clear behavioural outcomes following surgical castration in male dogs.

In conclusion, the researchers stated, "At present, dog aggression causes are not sufficiently well understood to allow an accurate prediction of the effect of gonadectomy on it. Dogs’ aggressive behaviour is not related to a single factor; instead, multiple environmental and genetic factors may contribute to its expression." (Palestrini C. et al, 2021)

Dictating the age of neutering and spaying a dog, going against scientific research and evidence is detrimental to animal welfare, health and well being. Veterinary professionals will be up to date and able to advise owners, who can also seek second opinions. Dog professionals, however, cannot advise, diagnose or comment in regard to health concerns under the veterinary act.

This post is not in regard to whether or not a dog should/shouldn't be neutered or spayed as I am not qualified to answer. My male dog is neutered as I did not intend to breed him and under vet advice, he was neutered and is a healthy dog from a health testing breeder. My rescue female dog is spayed under vet advice, she struggled with her first seasons and ran the risk of a phantom pregnancy. Each individual dog will have their history and behaviour assessed by a veterinary professional.

If your dog has behaviour changes and you have concerns, discuss this with your vet who will refer you to a veterinary behaviourist or clinical CCAB or APBC or ICAN qualified and assessed professional. Many behaviour changes are due to underlying health concerns, pain and illness so a vet check is always recommended by training and behaviour professionals.


Deborah L. Duffy and James A. Serpell (2006, November). Non-reproductive effects of spaying and neutering on behaviour in dogs. Proceedings of the Third International Symposium on Non-Surgical Contraceptive Methods for Pet Population Control. Alexandria, Virginia.

Parvene Farhoody (2010) Behavioral and Physical Effects of Spaying and Neutering Domestic Dogs (Canis familiaris). Masters thesis submitted to and accepted by Hunter College.

Palestrini C, Mazzola SM, Caione B, Groppetti D, Pecile AM, Minero M, Cannas S. Influence of Gonadectomy on Canine Behavior. Animals. 2021; 11(2):553.

Hsu, Y., and Serpell, J.A. 2003. “Development and validation of a questionnaire for measuring behaviour and temperament traits in pet dogs.” J. Amer. Vet. Med. Assoc., 223:1293-1300.

Serpell, J. and Hsu, Y. (2005). Effects of breed, sex, and neuter status on trainability in dogs. Anthrozoös, 18(3), pp.196-207.

Further research regarding neutering:


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