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Hormones and dog aggression

Hormones and dog aggression

What makes some dogs calm and chill, while other

Pitbulldogs flip out when they are in the presence  of dogs, people or other perceived threats in their environment?  Scientists all over the world are unravelling more and more mysteries of dog behaviour.  As a dog nerd, I was excited to find out that  recent research  at University of Arizona led by Evan MacLean linked the presence of two different hormones in the blood to behavioural changes.


MacLean and his collaborators looked specifically at oxytocin and vasopressin — hormones that are also found in humans — and found that they may play an important role in shaping dogs’ social behavior.

Why is this important to us dog owners? Well, Oxytocin (the love hormone) is found in higher levels in non-reactive dogs, in this case service dogs with no history of aggression.  Aggressive reactivity is found in dogs with elevated Vasopressin levels.



Blood levels of Oxytocin can be increased through bonding, food rewards and other positive experiences. In order to help aggressive dogs get on the right track with behaviour, veterinary scientists may soon be exploring ways to suppress the vasopressin system, so it doesn’t create as much of that hormone. But for most dogs, vasopressin can reduced, and oxytocin increased, simply by positive interactions with people.

“Previous work shows dog-human friendly interactions can create a release in oxytocin in dogs, and when dogs interact with people, we see that their vasopressin levels go down over time,” MacLean said. “These are bidirectional effects. It’s not just that when we’re petting a dog, the dog is having this hormonal response — we’re having it, too.”

Combative, dominance oriented approaches to treating dog behaviour simply don’t work unless it is repeated constantly over the life of the dog.  What a miserable way to live for both dog and human.


Evan Maclean’s studies of Oxytocin levels in dogs with aggressive behaviour will hopefully help to dispel some common mythology surrounding dog behaviour and training.  When we get dogs to calm down by using compassionate and kind training methods that include game based, bonding exercises, we can actually affect the levels of the hormones that cause bonding and aggression.  How cool is that anyway?