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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, 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 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 accompanied by the loss of hair, increased bodyweight, and lethargy may be a sign of hypothyroidism. Aggression following convulsions, when the dog appears absent, or when rapid mood changes occur may be the result of full or partial seizures. Damage to certain areas of the brain through disease such as hydrocephalus, tumors, thyroid issues 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. Dogs of any breed can be selectively bred for aggression intentionally or unintentionally.

Fear-Motivated Aggression

Dogs fearing for their own safety are more likely than confident dogs to bite another human or dog. The perceived threat to the dog can be real or imagined. Remember the threat is from the dog’s perspective. For example, a person could very innocently trying to reach over the dog to take a hold of their collar, but the dog may perceive the motion as intent to do harm, which leads the dog to react aggressively.

Protective Aggression

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

Territorial Aggression

Dogs may attempt to guard or defend their home or space. Territorial aggression includes barking and lunging at fences or from windows.

Resource Guarding

Dogs often attempt to protect resources 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

Predatory aggression is motivated by an animal’s drive to hunt and consume food. Often, predatory behavior is seen in dogs chasing smaller dogs, cats, or even young children.

Frustration Aggression

When a dog is prevented from doing something they want or forced to do something they do not want to do, they can become frustrated and direct aggression towards the nearest animal or person. The same concept applies to 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, examples of frustration aggression include aggression resulting from being 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 the 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 in attempt to prevent future pain. Unfortunately, animals often attack the person or animal nearest to them rather than only the thing actually causing pain. For this reason, it is a good idea to handle a dog in pain very cautiously. Many owners get bit 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. Social 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.

Teaching your dog to earn access to food or resources can help in some situations, such as asking for the dog to sit before opening a door. It is not recommended 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 acts aggressively for any of the above reasons but especially for fear-motivated aggression, they may learn 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 barking and lunging is effective. Similarly, if biting a hand 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.
  • See our handout 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 why the dog is behaving aggressively and toward whom. 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 sometimes the safest and most humane option for aggressive dogs which the owner cannot work with for whatever reason.   


For more tips on your pet's behavior and training, contact the Animal Humane Society's training school at 763-489-2217 or


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