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Dog Behaviour >> aggression

Aggression is a fairly common behavioural problem in dogs. It seems that most people assume that an aggressive dog is trying to assert dominance but I’ve found that this is often not true. Most aggressive dogs are fearful. Often a fearful dog then learns that the aggression works (i.e. makes people stop doing whatever the dog is not enjoying). Once they discover that aggression works, it becomes a learned behaviour as well. If you have an aggressive dog please see your veterinarian and/or seek referral to a veterinary behaviourist. Any person bit by a dog should seek medical care immediately due to the risk of rabies (fatal) and infections etc.

Due to the consequence of this behaviour the following information does not include a full treatment plan as professional help by a veterinary behaviourists or a veterinarian with a special interest in behaviour is highly recommended. Do not use trainers that focus on aversive/punishment based training as this will worsen the issue and put you at risk of injury and the dog at even great risk of euthanasia.

How is aggression defined. Well, I’ve yet to see a definition that is consistent. To me, it is any behaviour that suggests that the dog may bite. This can include staring, snarling, growling, and biting. This picture shows many of the warning signs – the tail is high and straight, erect hair on back, lips pulled back into a snarl and eyes very focused. Some dogs will freeze and show no other warning signals and then bite. Any of these symptoms are aggression. If a dog bites due to fear, although this is understandable, it is still a sign that this pet’s reaction to a fearful situation is to bite. It is not OK for a pet to bite when it is at the veterinary office as many owners think. This is a big warning sign that in any situation where the dog is fearful, it may bite. So, if this same dog is cornered by a child at home, the child is likely to get bit and could be seriously injured or even killed. This needs to be taken very seriously and dealt with early to try to rehabilitate the animal to prevent euthanasia or relinquishment of the pet and of course to ensure the safety of anyone interacting with the pet.

Never punish an aggressive dog. This will make a fearful dog more worried and dangerous and in some dogs punishment will result in a very fierce attack by the dog. Again, seek professional help.

This article will discuss:

1. Types of Aggression
2. Safety and Aggression
3. Dealing with Aggression
4. Prognosis

Types of Aggression:

There are several types of aggression and several different names for some of the classes. The following list only describes the most common ones very briefly:

  • Human Directed Aggression: This is any form of aggression directed against humans. These may be household members or strangers or sometimes just certain groups of people.
  • Fear Aggression: This type of aggression is seen in pets when they are fearful of a situation. They may try to flee, cower, growl, snarl, snap and bite in order to defend themselves. If the behaviour is left untreated the aggression will often worsen as the dog learns that being aggressive works. They will look less fearful and more assertive.
  • Interdog Aggression: Aggressive threats or fighting between dogs. This can be categorized as aggression against familiar dogs or unfamiliar dogs. Note, often rough play is interpreted as aggression. It is normal for dogs to snarl, growl, grab skin and pull. It is abnormal for another dog to not stop play when one dog yipes or rolls on its back.
  • Food-related Aggression or Possessive Aggression: This type of aggression is seen when the dog is eating or guarding a treat or a toy. This can be very dangerous if young children are in the house.
  • Redirected Aggression: This is aggression directed towards a person or pet that is not the initial source of the aggression. The most common example is when owners try to separate two fighting dogs and a dog bites a human. These dogs are in a highly aroused state and will bite quickly before really understanding what or why they are biting.

Safety and Aggression

If you have a dog that has bitten someone or shown aggression towards a person or another pet it is extremely important that you take precautions to prevent any further attacks until you can get help.  

  • If the dog is biting only in certain situations then ensure that the dog is kept away from these triggers.  This might include hugging, petting, grooming, etc. 
  • Most dogs will warn before biting.  These warnings should be heeded and the dog should not be punished.  If you can safely do so, lock the dog in a confinement area and do not interact until the dog is calm.  Make sure the pet has food, water and shelter of course. 
  • If the dog is food bowl aggressive the dog should be put outside while food is prepared and set in room that has a child proof lock.  The dog can then be let into the room and locked in until the food has been eaten.  The dog can then be enticed out of the room and confined in another room so the owner can remove the bowl. 
  • Cage or basket muzzle (pictured top right) or a Pro Guard Softie  Muzzle (bottom right) may be appropriate if it can be applied safely after a desensitization protocol.  They both allow the pet to pant and the cage muzzle also allows the pet to eat and drink so they are quite humane.   The pet still needs to be closely supervised and never left alone with children. The dog needs to be taught to accept and enjoy the muzzle. See the article on muzzles and headcollars.
  • The yard should be locked and the dog should not be allowed to roam outside without supervision. 
  • If the pet is aggressive towards visitors the dog should be confined when you have company.

If there is any doubt about your ability to keep your other pets or family safe, please discuss this with your veterinarian.

Dealing with Aggression

The treatment recommendations will vary depending on the type of aggression and the specific details of each case.  In any case, unfixed animals should have spay/neuter surgery as tendencies towards fear and aggression may be inherited.  A full physical exam and medical work-up should be performed as there may be a medical cause of aggression.  Brain imaging such as CT/MRI is highly recommended.  Referral to a neurologist may be suggested as well. If your dog is on a high protein dog food or if the aggression seemed to occur within a few months of a food change, a different diet might be suggested.

Once the diagnosis is made, the behaviour modification recommendations will often include the following components:

  • Ensure adequate exercise and mental stimulation.
  • Leadership Training (also called ‘Nothing in Life is Free’, ‘Work to Earn’, ‘Structuring Your Relationship’ – see Preventing Behaviour Problems handout for details)
  • Tranquility Training where the dog learns to relax in progressively more difficult situations.
  • If you have a fearfully aggressive dog do not pet or reassure the dog when it is nipping or growling at someone else.   Just stay calm and move the dog away from the situation. When the dog is calm ask for a sit and reward the dog if he/she complies.
  • Specific counter conditioning and desensitization programs.  These are exercises where the previously aggression provoking stimuli are very carefully reintroduced at low levels and the dog is asked to do a task such as sit and focus on the handler in this situation.  Again, details will vary depending on the problem and are not provided here as professional help should be sought out.


Behaviour problems are rarely cured and most have to be managed for life.  In the case of aggression, there is often controversy over whether it is even safe to try to change this behaviour.  In general, the prognosis is quite good in young pets or pets that have just recently begun showing aggression.  In dogs with severe aggression that has been occurring for some time the prognosis is less optimistic.   With any degree of aggression almost all the textbooks agree that the only way to 100% guarantee that the dog doesn’t ever bite again is to put the dog to sleep.   With severe aggression, this might be recommended especially if there is any doubt about how able an owner is to control and manage the situation and how committed he/she is to the behaviour modification process.  I do not mean to discourage or upset you but I think it is often difficult to be objective when you are emotional about a problem that involves a beloved pet.

If you read the bio on my dogs, Cody and Bud, you will see that I have dealt with aggression issues with both of these dogs.   We have to continue working on this and continue managing this for life.  It is a big commitment.  Bud’s aggression was actually quite easy to deal with.  He was younger and his aggression was less severe (he warned but never bit).  Cody’s aggression was very difficult to deal with and at first it was hard to identify his triggers (he bit and did not warn).  He has improved greatly and will approach and greet strangers in a friendly manner and allow me to groom and brush his teeth. This experience has given me a new appreciation for, and understanding of the risks that owners face in these situations.  I implore you to protect your family while trying to do your best for your pet.  Please get professional help as soon as possible.

Thank you for your interest in my website and I hope this information was useful. If you have an aggressive dog know that there are others out there who have gone through difficult situations like this and you are not alone. 

Best wishes. 

Dr. Liana Mawer

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