After A Lot Of Researches, Studies Finally Reveals What Makes The Dogs Aggressive!


Number of people are hospitalized every year because of dog bites. The aggressive behavior is a huge reason dogs are put in shelters or put down. The biology behind the canine aggression has been studied and the reason is found in the hormones Vasopressin and Oxycontin.


What Is Aggression?

The term “aggression” is a variation of multiple behaviors that happen for a number of reasons in different situations. Every wild animal is aggressive when they are guarding their territories, defending their offspring and protecting themselves. This is typical for species that live in groups and it includes people as well. Often when there is found a threat of aggression, aggression is used back to keep peace and negotiate social interactions.

To say that a dog is “aggressive” can mean a whole host of things. Aggression encompasses a range of behaviours that usually begins with warnings and can culminate in an attack. Dogs may abort their efforts at any point during an aggressive encounter.

Fear and Aggressive Dogs

For many fear-aggressive dogs, it is a lack of adequate dog exercise that is the root of the dog problem behavior. Dog exercise burns the dog’s excess energy and helps maintain the dog’s healthy state of mind. This is important because, in order to talk to the mind, you need to remove the energy from the body.

Dog on Dog Aggression

aggression dog on another dog

With dog on dog aggression, your dogs are asking you to step up as the pack leader. Animals select pack leaders because they instinctual know who is strong and who can best lead them. An animal pack leader is concerned for the pack, not for himself. His natural instincts are protection and direction for the entire pack. It’s an unselfish role and an instinctual role. And in return, the pack completely trusts the pack leader. You need to earn your dogs’ trust, loyalty, and respect before the dogs will look to you as their leader and you do this by giving them rules, boundaries, and limitations.

Once your dog sees you as their pack leader, the dog on dog aggression will stop as they stop fighting for dominance because you will be their calm-assertive pack leader.

The Leash-Aggression Issue

walking with dog

Dogs with what is known as “leash aggression” may bark, growl or lunge at other dogs during walks, setting the scene for a tense and potentially dangerous interaction. So why do some dogs lash out on the leash while others don’t? Hormones may be to partly to blame, according to new research led by the University of Arizona’s Evan MacLean.

MacLean and his collaborators looked precisely at oxytocin and vasopressin which are hormones that are also found in humans. They have found that they may be really important in shaping a dogs’ social behaviour. MacLean was interested in oxytocin and vasopressin, sometimes thought of as “yin and yang” hormones, because of the growing research on their role in the biology of social behaviour.

Oxytocin, which is significant in giving birth and nursing, is sometimes called the “love hormone,” as its levels in humans have been shown to increase when we hug or kiss a loved one. Vasopressin is a closely related hormone involved in water retention in the body. In contrast to oxytocin, it has been connected to aggression in humans, with previous research suggesting that people with chronic aggression problems have high levels of vasopressin.

The Experiment

the experiment

For the current study, MacLean and his collaborators recruited pet dogs of varying ages, breeds and sexes, whose owners reported struggles with leash aggression. For each aggressive dog recruited, the researchers found a non-aggressive dog of the same sex, age and breed to serve as a comparison.

During the experiment, each dog was held on a leash by its owner. Across the room, an experimenter played audio of a dog barking behind a curtain, before pulling back the curtain to reveal a lifelike dog model with a human handler.

The dogs in the study were presented in the same way with everyday noises and three common objects — a cardboard box, trash bag and an inflated yoga ball.

The dogs’ responses and hormone levels were measured before and after the interaction.

While none of the dogs in the study reacted aggressively toward the box, bag or ball, many of the dogs in the leash aggression group had aggressive responses to the model dog, including barking, growling and lunging.

The dogs that reacted aggressively showed higher levels of total vasopressin in their systems, suggesting a link between vasopressin and aggression.

The researchers did not observe differences in oxytocin levels between the two groups of dogs. However, when they compared the oxytocin levels of the pet dogs in the study to a group of assistance dogs, which are specifically bred to have non-aggressive temperaments, they found that the assistance dogs had higher levels of oxytocin and higher oxytocin-to-vasopressin ratios. This supports the idea that oxytocin may help inhibit aggression in dogs.

Seeing high oxytocin levels in assistance dogs is completely consistent with their behavioral phenotype — that they’re very, very friendly dogs that are not aggressive toward people or other dogs,” MacLean said.

It would be reasonable to think that if vasopressin facilitates aggression, you could develop pharmaceuticals that could target the vasopressin system to help in cases where dogs are really aggressive,” he said. “Oxytocin and vasopressin are being used extensively as therapeutics in humans right now. Regulation of the oxytocin system has been implicated in things ranging from autism to schizophrenia to post-traumatic stress disorder, and there are clinical trials looking at administering oxytocin as a drug to create some kind of behavioral response. It’s interesting to think that maybe some of these same therapies we’re trying with people could be useful in dogs.

As to why some dogs have higher levels of vasopressin, life experience may be a factor, MacLean said.

There’s a lot of work showing that experiences in your lifetime can change the way hormones function,” MacLean said. “For a lot of dogs that have aggression problems, the owners report that the onset of the aggressive symptoms happened after some sort of traumatic experience. Often it was that the dog was attacked by some other dog and is in a hyper vigilant state after that event — almost like a post-traumatic reaction.


There is a way to boost dogs’ oxytocin levels and decrease vasopressin is through friendly dog-human interactions. And the effect extends to people as well.

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.