Aggression in Dogs: The Roles of Oxytocin and Vasopressin

A new study shows these hormones can shape both affiliation and aggression.

Posted Oct 05, 2017

A recent study on aggression in dogs by University of Arizona professor Evan MacLean and his colleagues called "Endogenous Oxytocin, Vasopressin, and Aggression in Domestic Dogs" caught my eye because of my long-standing interest in the social behavior of dogs. Oxytocin is often referred to as the "love" hormone, although the case for the extremely close relationship between positive behavior and oxytocin is often overstated. In contrast to oxytocin, vasopressin, also referred to as antidiuretic hormone (ADH), has been linked to heightened aggression in humans, and now, for the first time, in dogs. 

It might surprise people that we don't really know all that much about the hormonal bases of social behavior in dogs. To wit, as the researchers note, "Aggressive behavior in dogs poses public health and animal welfare concerns, however the biological mechanisms regulating dog aggression are not well understood." In the United States alone there are around 4.5 million dogs bites each year, with about half involving children. The number of dog bites sustained by youngsters has been decreasing in the past decade. For more detailed multidisciplinary information on dog bites please see "Dog Bites: Comprehensive Data and Interdisciplinary Analyses". 

The complete text of "Endogenous Oxytocin, Vasopressin, and Aggression in Domestic Dogs" is available for free online, and an excellent summary of this landmark study can be found in an essay by Carrie Arnold titled "Why Are Some Dogs More Aggressive?" Basically, Dr. MacLean and his colleagues began studying dogs who showed unprovoked aggression towards dogs and observed how they responded to non-aggressive dogs of the same sex, age, and breed. They measured levels of oxytocin and vasopressin before dogs were exposed to one another. When the dogs were walked by stuffed dogs, they displayed aggression. Ms. Arnold writes, "the aggressive dogs growled, lunged, and barked more at the stuffed dogs than their non-aggressive counterparts. They also had significantly more vasopressin in their blood."

What's very appealing about Dr. MacLean's study is that he and his colleagues also studied service dogs to learn how they behaved in the presence of a threatening unfamiliar human and unfamiliar dog. Overall, these dogs were calmer and showed more oxytocin present in their blood than non-service dogs. Ms. Arnold writes, "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."

Teasing Out Cause and Effect and Understanding Individual Dogs

Studies such as this have are very interesting in their own right and also have important practical applications. For example, while it's not known if vasopressin causes or is the result of aggressive behavior, we now know something about the underlying bases for this behavior. When cause and effect are sorted out, this might lead to ways to control out-of-control and inappropriate aggression. And, while aggression seems to be much less common than affiliative or positive (prosocial) behaviors in dogs, it still is an adaptive response in certain situations and is clearly expressed in a wide variety of other diverse animals, including humans. 

It's worth quoting the conclusion to the original research paper because the authors clearly present why their study is so important. They write, 

Ultimately, dog aggression is a normal and adaptive social behavior, but expressed in the wrong contexts, or to an extreme extent, its consequences jeopardize the welfare of both humans and dogs in our society. It is likely that dog aggression can be motivated by diverse psychological states, including fear and anger. These emotional processes may be facilitated by, or produce effects on, OT and AVP signaling in the brain. Thus, it is important to consider dog aggression at multiple levels of analysis, addressing both the cognitive processes (e.g., appraisal, learning, inhibition), and underlying physiological mechanisms, which mediate these behaviors. The studies presented here suggest that OT and AVP may play important roles in these socioemotional processes, and set the stage for future work evaluating whether treatments and interventions for aggression can be improved by considering the roles of these neuropeptides. Ultimately, we hope that these investigations will lead to increased knowledge of the biology of social behavior, promote human and animal welfare, and help to preserve the unique and long-standing relationship between humans and dogs.

Please stay tuned for more research on all aspects of the social behavior of dogs and other animals. I look forward to research that can disentangle cause and effect in the relationship between hormone levels and aggression, the results of which will make life more pleasant for dogs for whom aggression is a normal response because of who they are as individuals.

It's essential to understand dogs as individuals because a dog's own personal experiences surely can play a significant role in how she/he responds to various situations, as can the way they've been trained. What appears to be inappropriate may be fully understandable when the individual dog's point of view is taken into account.

All in all, being able to extinguish aggression when it isn't an appropriate response would be a win-win for dogs and humans.

Marc Bekoff’s latest books are Jasper’s Story: Saving Moon Bears (with Jill Robinson); Ignoring Nature No More: The Case for Compassionate Conservation; Why Dogs Hump and Bees Get Depressed: The Fascinating Science of Animal Intelligence, Emotions, Friendship, and Conservation; Rewilding Our Hearts: Building Pathways of Compassion and Coexistence; The Jane Effect: Celebrating Jane Goodall (edited with Dale Peterson); and The Animals’ Agenda: Freedom, Compassion, and Coexistence in the Human Age (with Jessica Pierce). Canine Confidential: Why Dogs Do What They Do will be published in early 2018. Learn more at marcbekoff.com.

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