The Role of Hormones in Aggressive Dogs

Barbara Sherman, clinical professor of veterinary behavior and Margaret Gruen, adjunct assistant professor at the NC State College of Veterinary Medicine, are co-authors of a study published in the journal Frontiers in Psychology about the role of two hormones in aggressive dog behavior.

Dogs bite about 4.5 million Americans each year — about half of them children — according to the Centers for Disease Control, resulting in about 2 million dogs euthanized each year. Yet, as stated in the article, “we know relatively little about the psychological and biological factors underlying dog aggression.”

The study is the first to examine the roles of two hormones, oxytocin and vasopressin, in influencing both aggressive and non-aggressive behavior in domestic dogs. The CVM collaborated with the University of Arizona, Indiana University and Duke University on the study.

The hormones oxytocin and vasopressin influence canine social behaviors and aggression. Service dogs, bred for their placid temperament, have significantly higher levels of oxytocin in their blood than the average pooch. Those dogs that were more aggressive towards other dogs, however, had more vasopressin.

Researchers compared the hormone levels of dogs with a history of aggressive behavior to other dogs with no history of aggression. The NC State Veterinary Hospital’s behavior medicine service recruited and observed the behavior of the dogs, which were recorded on video. The dogs were given plush models of dogs to trigger an aggressive response. Aggressive dogs had higher plasma vasopressin levels than control group dogs and tended to respond aggressively to the models.

The study also found that service dogs, specifically bred for their calm and easy-going temperament, had especially high levels of oxytocin, a hormone associated with familial bonding after childbirth. This contrasts with the dogs with a history of aggressive behavior and elevated level of vasopressin.

If vasopressin is a key factor in determining aggression in dogs, it could open new possibilities for managing behavior. However, the next step in the research process is determining if the hormone drives behavior, or is merely a result of existing aggressive tendencies.

~Steve Volstad/NC State Veterinary Medicine