Neutering in dogs – does it change their social behavior?

Right up until a few years ago, it was common practice to neuter a dog “prophylactically.” There were many reasons for this, including to prevent supposed misbehavior. These days, though, neutering is a hotly debated topic.

Proponents still hold that sterilization is a good way to treat and prevent behavior problems, including aggression. On the other side, there are indications that neutered dogs may be even more aggressive than those that have not been “fixed.” Systematic scientific studies showing a link between aggression and neutering are rare, however.


It is generally very difficult to take an all-encompassing view of this context from a scientific perspective, since different forms of aggression vary widely. For example, you might assume that sexually motivated aggression, if anything, would decline as a result of sterilization. But other forms of aggression, such as territorial aggression or defending resources, are probably not affected by this kind of intervention. Unfortunately, there are no studies to date that consider the specific influence of neutering on different motivating factors behind aggression. As a result, I can only cite studies that approach this topic from a more general standpoint.



One recent study investigated the extent to which aggressive behavior toward familiar humans, strangers, or fellow dogs differed in dogs that had been sterilized at different ages. The data are based on a questionnaire that is now in very widespread use in studies of dog behavior and has been subjected to thorough review. Known as the C-BARQ (Canine Behavioral Assessment Research Questionnaire), this questionnaire is typically completed by the dog’s owner. The evaluation included 13,795 questionnaires in which dogs displayed aggressive behavior toward familiar people, 13,498 with aggressive behavior toward strangers, and 13,237 that involved aggressive behavior toward other dogs. All of the questions on the C-BARQ that concern aggressive behavior were evaluated, and median values were calculated on this basis. The results for dogs that did not show any aggression at all were compared with those for dogs with moderate to high aggression. There was also a comparative analysis of the data for intact dogs and those on dogs that had been neutered at the age of six months or less, seven to 12 months, 11 to 18 months, and over 18 months.



A link between sterilization and aggressive behavior?


The study results did not show any link between sterilization per se or the age at the time of the operation and aggressive behavior toward familiar humans and other dogs. However, dogs that were neutered at ages between 7 and 12 months were slightly more likely to display moderate to strong aggression toward strangers.


If different factors that can trigger aggressive behavior are taken into account, there does not seem to be any connection between neutering and aggressive behavior toward familiar people and other dogs. The only finding was a minimal increase in aggression toward strangers.



Other studies have also shown that early sterilization in particular can cause undesirable behavioral changes. A questionnaire study conducted by Zink and colleagues in 2014 asked Viszla owners about their dogs’ health status. It showed that animals that had been neutered at less than six months of age were at higher risk of behavioral anomalies in comparison to other dogs that had not undergone the operation.


Another study documented the responses of female dogs to approaches by strangers and other dogs. Female dogs that were neutered at the age of five to ten months responded with significantly greater aggression in these situations five months later on than their littermates that had not been operated on.


On the whole, these results show that sterilization is not suitable as a means of treating or preventing aggression problems. On the contrary, in fact – the results indicate that the operation can even increase a dog’s aggression levels under certain conditions.


In male dogs, these behavioral changes can also be triggered by what is known as a castration chip, or “chemical castration.”  In this procedure, a hormone chip is implanted in the dog, making him infertile for a certain period (typically six to 12 months). But especially in the case of uncertain and fearful dogs, people should consider this treatment carefully, since it could result in greater aggression. The manufacturer itself expressly warns as follows in the use information: “Dogs with sociopathic disorders and episodes of intraspecies (dog to dog) and/or interspecies (dog to other species) aggression should therefore not be sterilized either surgically or through the use of an implant.”

If there are compelling reasons to seek sterilization anyway, this kind of “chemical castration” can be used to test whether possible undesirable behavioral changes occur, since its effects occur for a limited time only, so the possible behavioral changes are temporary as well.


In light of the increasing indications that neutering dogs can have negative effects, this intervention should be considered carefully, and decisions should always be made on a case-by-case basis.

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