Pexels/Torsten Dettlaff.

Behavioural problems in male dogs may be affected by how early in their life they are desexed, according to a study published today in PLOS ONE. The study even raises questions about whether we should encourage the routine desexing of male dogs at all.

Desexing is where a male dog’s testicles are surgically removed. It’s a procedure advocated in many countries, including Australia. The chief reasons are population control and prevention of certain health conditions, such as testicular cancer.

But many veterinarians also advise desexing to avoid and address behavioural problems such as roaming, mounting, and aggression towards other dogs.

Possible effects of routine desexing on male dog behaviour have not been examined closely until recently.

The PLOS ONE study reports on the behaviour of 6,235 male dogs that were desexed for reasons other than behavioural management. These reasons include the absence of any intention to breed, a requirement of the vendor, or for perceived health benefits.

It follows a recent report showing no evidence that desexing at any age altered aggressive behaviour towards familiar people or strangers in male or female dogs.

The age of desexing

When surgical desexing first became a common practice around 50 years ago, male dogs were typically desexed at around six months of age.

But a push for early-age desexing arose, for two reasons: the pressing need to reduce the unwanted dog population,and to avoid owners forgetting to present their maturing dog for desexing.

These days, desexing can be performed from as early as eight weeks of age, and at a minimum of 1kg bodyweight.

Our study considered the effects on everyday behaviour of desexing male dogs and, in turn, preventing them from going through puberty, reaching sexual maturity, or living with sex hormones. Puberty in male dogs varies with breed and size, ranging from 6 to 15 months.

We collected data from the online Canine Behavioral Assessment and Research Questionnaire (neatly abbreviated to C-BARQ). C-BARQ allows owners from all over the world to report on their dog’s behaviour. It has gathered data on more than 80,000 dogs.

We focused on male dogs, and calculated each dog’s percentage of lifetime exposure to sex hormones. This was based on the reported age at which he was desexed and the age at which his behaviour was described by his owner via C-BARQ.

Timing can matter

We found male dogs with an increased lifetime exposure to sex hormones (that were desexed later in life) were associated with more indoor urine-marking and howling when left alone at home than their earlier desexed counterparts.

But significantly, there was less reporting in these later desexed dogs of at least 24 other problem behaviours. Examples include barking persistently when alarmed or excited, and showing signs of fear and anxiety in response to sudden or loud noises (vacuum cleaners and thunderstorms etc.).

Our study underlines the need to consider the optimal time for desexing of male dogs but also raises questions about routine desexing of male dogs.

This new information adds to and supports the need to discuss ethical concerns associated with routine desexing of male dogs, and possibly to review blanket recommendations about desexing.

Our new findings suggest that a dog’s tendency to show numerous behaviours can be influenced by the timing of desexing. They suggest that dog behaviour matures naturally when sex hormones are allowed to have their effect.

This aligns with our previous studies on the so-called super-trait of boldness, showing that entire dogs of both sexes are bolder than desexed dogs, and that boldness decreases with ageing.

If boldness predicts less fearful behaviour and more sociable behaviour with humans and dogs, it would be desirable in companion dogs. The potential for individual boldness to change during life raises questions about whether desexing may contribute to problem behaviours associated with this super-trait.

It may be that early-age castration renders male dogs more dependent on the company and social support of others. Perhaps fear, anxiety and aggression are manifestations of canine immaturity.

Keeping out of the pound

The beneficial effects of desexing for dog welfare are underpinned by the need to reduce the number of unwanted companion animals. It is estimated that more than 43,000 dogs are euthanased annually in shelters and pounds across Australia.

But shelters are inundated by dogs that are most commonly surrendered because they display undesirable behaviour. A 2013 study found 65% of owners reported a behavioural reason for surrendering their dog, with 48% reporting that at least one behaviour strongly influenced their decision to surrender.


Read more: Want to get fit? Your dog may be your perfect training partner


The current findings present a paradox. Desexing may reduce the numbers of unwanted dogs at large. But it may also increase the likelihood of problem behaviours that reduce the appeal of the desexed dogs and make them more vulnerable to being surrendered.

We want to be very clear that this is not to say that messages about desexing have been wrong. Rather, they need to be considered as part of a complex decision-making process that takes multiple factors into account.

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