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Aggression in dogs

Aggression in dogs is cause for concern in many dog owners.  Aggression is defined as the threat of harm to another individual involving snarling, growling, snapping, biting, barking, and/or lunging.  Understanding the contributing factors in aggression can often help in the treatment of aggression.  The most common reason for aggression is fear, but occasionally other factors contribute to aggression.  Aggression, whatever the cause, is a very serious issue that should only be treated by working with a veterinary behaviorist that can work with you individually on behavior modification techniques. 

Reasons for aggression

Aggression due to Medical Problems
Occasionally, aggression in dogs can be the result of a medical issue.  Aggression that is accompanied by the loss of hair, increased bodyweight, and lethargy may be a sign of hypothyroidism.  Aggression that appears with convulsions or when the dog has an absent appearance or rapid mood changes may be the result of full or partial seizures.  Damage to certain areas of the brain through disease such as hydrocephalus (more common in toy breeds and brachycephalics), tumors, or trauma can also result in aggression problems.  A consultation with your veterinarian can diagnose these conditions and offer medical treatment as necessary. 

Genetic Predisposition
Some dogs are genetically predisposed to aggression.  This may be the result of either the medical conditions mentioned above or selective breeding for dog-to-dog aggression found in “protection” or “fighting” breeds.    

Fear-Motivated Aggression
Dogs that fear for their own safety are often the most likely dogs to bite another human or dog.  The perceived threat to the dog can be real or imagined.  Remember that the threat is from the dog’s perspective.  That can mean that a person could have been very innocently trying to reach over the dog and take a hold of their collar, but the dog may have perceived this as intent to do harm to them, which leads them to react aggressively.   

Protective Aggression
This most often happens when a mother protects her young pups.

Territorial Aggression
Dogs may attempt to guard or defend their home or space.  This can include barking and lunging at fences or from windows. 

Resource Guarding
Dogs often attempt to protect resources that they control.  A dog may guard valuable resources such as food, toys, and a bed, but they may also guard less valuable resources such as bits of trash.  In guarding these resources, they can use techniques such as growling, snapping, and even biting to maintain the control over the resource.

Predatory Aggression
This type of aggression is motivated by an animal’s drive to hunt and consume food.  This can be seen particularly in dogs chasing smaller dogs, cats, or even young children. 

Frustration Aggression
When a dog is prevented from doing something that they want or forced to do something that they do not want to do, they can become frustrated and direct aggression towards the nearest animal or person.  This same idea can be seen in people.  When a person puts money into a vending machine and no food or drink comes out, they become frustrated and often turn to aggression (hitting, kicking, or pushing the vending machine).  In dogs, this can be seen in cases where they are physically held back by their collar or forced into a kennel.  Another form of frustration aggression is redirected aggression.  In redirected aggression, a dog may become aroused by a stimulus (such as a doorbell or dog outside the window) and are prevented from directing aggression at that stimulus and instead turn and attack another dog or their owner.

Pain-induced Aggression
Animals of a variety of species attempt to protect themselves by responding aggressively when they feel pain.  This typically helps them to prevent future pain.  Unfortunately, animals often attack the person or animal nearest to them rather than only the thing that actually caused them pain.  For this reason, it is a good idea to handle a dog that is in pain very cautiously.  Many owners have been bitten while attempting to help their injured dog.  Additionally, the use of training devices that inflict pain on animals, such as prong collars, choke chains, and e-collars, are not recommended because they may lead the animal to become more aggressive to stop the pain. 

Social Aggression
Dogs naturally live in groups, typically including both other dogs and humans.  As in any group situation, leaders and followers naturally emerge.  The leaders tend to take charge of a situation and the resources available.  Just as in human situations, if more than one individual wants to be the leader, fights can break out.  When a lower ranking individual attempts to take control of a situation or a resource (e.g., food bowls or spots on the couch), the leader (or the one who perceives themselves as the leader) will attempt to regain control.  This type of aggression is most common in intact male dogs, but can occur in females and neutered dogs as well.  Neutering a male dog along with behavioral training may help to reduce social aggression. 

Practicing good leadership skills by using basic obedience to have the dog earn access to toys or food can help in some situations.  It is not recommended that you use physical force such as scruff shakes or “alpha” rolls.  These do not typically lead to a respectful stable relationship with your dog and often escalate the aggression even further.

Learned Aggression
Once a dog has acted aggressively for any of the above reasons but especially for fear-motivated aggression, they may learn that the best way to get what they want is to repeat the aggression.  If barking and lunging at the mailman gets him to leave, then the dog will learn that barking and lunging is effective.  Similarly, if biting at a hand that is reaching for them gets the hand to go away, they will quickly learn to bite to remove unwanted contact.

What to Do

  • Talk with your veterinarian about the possibility of a medical cause for the aggression particularly if you notice other symptoms. 
  • Seek professional help.  Call a Veterinary Behaviorist to get help with behavioral modification of the aggression.  Do not expect your dog to get better on their own or just grow out of it.  Aggression is a very serious problem.
  • Read our article on Managing an Aggressive Pet to help you cope until you can seek professional help.

Should I Work with My Aggressive Dog?
This is really a personal decision and depends on the amount of time and money you are willing to invest in the dog.  It can also depend on who the dog is being aggressive towards.  If the dog is only aggressive towards strange dogs or people, it may be easier to manage the situation than if the dog is aggressive towards your children.  If you do not have the time or money to work with the dog, you will need to consider options such as surrendering the dog to the breeder or shelter where you got them.  Before you consider re-homing the dog, you will need to be open and honest about the dog’s aggression issues to ensure the safety of everyone involved and you may still be held liable for any future behavior of the dog.  Euthanasia is always a humane option for aggressive dogs which the owner cannot work with for whatever reason.   

This material is copyright of Animal Humane Society and can only be used with written permission.