Many owners spay or neuter their dogs, an euphemism for a castration. Sterilization rarely happens in dogs, as in most cases not only the hormonal glands are removed, but also the reproductional organs (the womb and testes) that are necessary for reproduction. The removal of the hormonal glands stops any sexual induced behaviour in castrated dogs. Castration is seldom a topic of discussion. If there's no wish to breed a litter, people will often automaticly decide to have the dog castrated. The following motivations are often a reason to spay or neuter a dog:
• Fear of diseases (particularly cancer) in intact dogs.
• Less hormonal behaviour, thus easier to raise and train the dog. Less scent marking and hormone driven behaviour in both males and females..
• Improved social behaviour toward other dogs.
The latter is a very common reason. After all, intact males are presumed to be more aggressive and castration would make them a lot more mellow around other dogs. Many websites, invariably belonging to veterinarian clinics, say the same. It "reduces aggressive behaviour towards other dogs. (...). For the owner a walk with a neutered male is a lot more pleasant."
But is that really the case, can we always assume that? According to a few large studies, the answer is no. This includes two studies, both of which used the Canine Behavioral Assessment and Research Questionnaire (usually abbreviated as the C-Barq), a widely used scoring list for dog behaviour where the dog is evaluated on the basis of more than 100 questions. Large groups of dogs were used in both researches, providing reliable figures.
In a study by Deborah Duffy (University of Pennsylvania) 3.600 dogs were included. The research by Farhoody (Hunter College in New York) even included 11.000 dogs. The results summarized: aggressive behaviour did not decrease, rather the opposite. The dogs were significantly more anxious. Only marking decreased significantly.
Duffy saw some striking differences between intact and neutered dogs. Neutered females prove to exhibit aggressive behaviour towards strangers as well as their owners more often, the differences were significant. Equally striking, the females were also much more anxious and sensitive to touching. Both females and males were found to be much more interested in food, begging has increased in both sexes.
Aggressive behaviour towards other dogs was breed specific. Some breeds including the Yorkshire Terrier, the Siberian Husky and the West Higland White Terrier had less dog-dog aggression. The Dachshund, the Springer Spaniel and Golden Retriever showed more targeted dog aggression. In average all breeds showed that dogs, male and female, had more aggression towards other dogs.
Another behavioral trait that changed was rolling in and eating faeces, which also rose in neutered dogs. Barking and excessive grooming was more common in neutered dogs than in intact dogs. Incidentally, as Duffy points out, the behavior was not of a nature that it was really problematic behaviour, but she advises to use alternative methods of birth control, and to give owners a more precise expectations. "No, your dog is not necessarily easier if he or she is neutered".
Farhoody also comes to roughly the same conclusions. "There was a significantly higher aggression score in neutered dogs compared to intact dogs regardless of the age at which the dogs were neutered, in the male dogs." he writes. In females it is different. Bitches that are castrated before reaching the age of one year score significantly higher in terms of aggressive behavior than intact females. Farhoody also concluded that neutered dogs, male or female, were more anxious than intact dogs, regardless of the age at which they had their castration.
Partly because of this kind of research, it is better to think twice before going to the vet to have a dog spayed or neutered. Medical studies have already shown that castration has a negative impact on several joint disorders, and that it doesn't always decrease chances of cancer.