Spaying and neutering are attributed with many benefits, including better canine health and decreased mounting and roaming behaviors, as well as reduced aggression. Sterilization repeatedly has shown to have both positive and negative physical effects on either sex of dog. While spaying or neutering can indeed have some effect on hormone-related behaviors, it is not guaranteed that a dog will be less likely to bite if it has been sterilized.
Spaying and Neutering Surgery
Both spaying and neutering remove a dog’s ability to reproduce. Spaying is a major surgical procedure. It consists of opening a female dog’s abdomen and removing her uterus and ovaries. Neutering a male is less invasive than spay surgery. It involves removing the male’s testicles through an incision made in his scrotal sac.
Spaying and Aggression
Because spaying removes a dog’s uterus and ovaries, it also removes her body’s ability to create a hormone called progesterone. According to dog behaviorist Stan Rawlins, progesterone is a “natural calming hormone and serotonin uplifter.” Because these things that calm a female dog are reduced or suppressed, it is possible for spaying to increase aggression and may cause greater “reactivity” in spayed female dogs, which may include barking and lunging at people and other animals. Increasing these things also increase the likelihood that your female dog will bite after she has been spayed.
Neutering and Aggression
More behavioral changes are seen in the male dog than in the female dog. Removing a dog’s testicles reduces the amount of testosterone his body produces, which in turn reduces his need to mount and to urine mark. The reduced testosterone can result in reduced aggression between dogs, even between neutered dogs and non-neutered dogs. Other forms of aggression do not seem to be affected, however.
Dog to Human Aggression and Biting
Spaying female dogs can increase reactivity, which may result in more opportunities to bite. Neutering male dogs makes no significant difference in terms of biting, in that biting is not a hormonal behavior. Rather, most biting results from fear and anxiety, which training, not neutering, affects. Generally, neutering is not likely to have a great deal of effect on reducing aggression or eliminating aggressive behavior. If a dog is displaying aggression before being neutered, training should also be part of the efforts to prevent biting and other aggressive behaviors.