Aggression is a normal form of communication for animals and a common life-threatening behavior problem in pets. The problem is not only dangerous for humans or other animals to which the aggression is directed, but left unresolved, aggression is a common reason for pets to be euthanized.

Staring, growling, hissing, lunging, snapping, swatting, and biting are all behaviors described as aggression. Many conflicting opinions and misinformation can be found online, on television, and in books describing the motivations behind aggressive behaviors. However, scientific research tells us that fear, anxiety, and pain are often the most common reasons why animals will use aggression.

Getting Started

When an animal first shows aggression, a thorough physical exam, neurologic exam, and orthopedic exam by a veterinarian will help to rule out underlying medical conditions that may be stimulating the aggressive behavior. A complete blood count, serum biochemistry profile, and urinalysis help to evaluate organ function along with a thyroid profile if supported by other findings, to rule out hypothyroidism in dogs and hyperthyroidism in cats.

Troubleshooting Beforehand

Safety is a top priority when living with or working with aggressive animals. Identifying and avoiding the triggers for aggression when possible will reduce the opportunity to practice the behaviors and help your pet feel safe. Recognizing body language cues of fear, anxiety, and stress such as ears back and flat against the head, head down, tail tucked, lips tight and drawn back, leaning away or crouched position, avoiding direct eye contact, licking of the lips, yawning, dilated pupils, and hair standing up (piloerection) will help to increase safety when you recognize these and indicators of a potential aggression response from your pet. Many people are under the misimpression that a dog wagging its tail is happy; this is not true. Tail wagging actually signals a willingness of the dog to interact, be that through happy interactions like play or petting, or in the case of an aggressive animal, through biting.


Treating aggression can be challenging, and often these animals are not cured, but rather managed; it all depends on the underlying motivation.

  1. The procedures below can be helpful, but they do not replace expert help for an individual animal. Contact your veterinarian for referral either to a trained veterinary behaviorist, or to a reputable animal trainer. This is important because many so-called trainers are not actually equipped to help, and some recommendations can be counterproductive.
  2. The first step of treatment often involves increasing human safety by teaching the dog to wear a basket muzzle (Baskerville or Italian Basket Muzzle; see Figures 1 and 2). If desensitized and counter conditioned properly, dogs can learn to love wearing a muzzle. Some will even ask to put it on. The openness of the basket helps to reduce severity of bites and allows delivery of treats during training and behavior modification sessions.

  3. Identifying potential triggers and avoiding them or the use of desensitizing and counterconditioning to reduce fear associated with these triggers can also be of value.

  4. Dogs and cats can react to a variety of different triggers such as other dogs, other cats, certain people, children, noises, bicycles, cars, and situations. For the dog that is aggressive to visitors, putting the dog away in a crate or behind a closed door with a yummy treat such as a food-stuffed Kong or puzzle toy will help remove the dog from situations that make him or her uncomfortable. The long-lasting treat or toy helps to condition the dog to form more pleasurable or positive associations with visitors.

  5. For dogs and cats aggressive to other cats in the household, separation is key to managing and reducing aggression.

  6. For dogs that are aggressive to other dogs on and off leash, avoiding dog parks or walking the dog in a location where other dogs are rarely present may be required. Teaching the dog to “look” or “watch” you (eye contact) instead of the other dog or person on walks will help to redirect the dog and when paired with yummy treats, form more positive associations with these triggers.

  7. Tools such as head collars and front clip harnesses give you better control of your dog on walks and help redirect your dog’s focus away from the trigger as he or she continues to move on past. These can also be used in the house attached to a 6- or 4-foot (2- or 1.3-meter) leash if needed for extra safety. Retractable leashes should never be used with an aggressive dog of any size: they provide no control and can be scary if dropped or snapped.

  8. For cats and dogs, positive reinforcement training is excellent for improving communication and teaching behaviors used for redirection in a nonconfrontational way.

  9. In the house, dogs and cats can be taught to stay on a mat for various periods of time. This mat is a very useful place to redirect your pet if you notice behaviors indicating an impending fight between household pets or if your pet needs to be safely removed from the couch, chair, or bed without confrontation.


Punishment in the form of shock collars, water bottles, cans of pennies, alpha rolls, spanking, or even just yelling “no” is often counterproductive with aggression. It is much more effective to teach and reward your pet for acceptable behavior than it is punishing the ones you do not desire. The use of corrections can confuse and frustrate dogs and cats, making them more fearful or anxious and increasing the likelihood that they will bite.

As with other behaviors, early detection and intervention are crucial in the management and treatment of aggression. Early socialization along with fun and pleasurable interactions with humans and other animals will help dogs and cats experience less fear or anxiety when presented with novel stimuli in their environment. It gives them the opportunity to form better coping skills.

Basket muzzle seen from the dog’s perspective. The open spaces allow breathing and make the muzzle comfortable.
Basket muzzle being placed on a dog. Note the open spaces that allow the tongue to pass through and receive a treat.

Frequently Asked Questions

Are medications available to modify my pet’s aggression?

Medications are available to modify some behaviors and should be used only in conjunction with a complete behavior modification program under the direction of a veterinarian. Contact your veterinarian for further guidance.

Can my pet’s aggression become worse over time?

Yes. This is why it is important to identify triggers that, without your knowledge, may be triggering aggression. By managing your pet’s environment and preventing exposure to triggers, aggression is less likely to occur.

Is there ever a time when a repeatedly aggressive dog or cat can be considered cured of his/her aggression?

Unfortunately, an animal that is aggressive is never considered cured. However, with proper management, safety improves for all involved. Early intervention and an understanding of body language cues reduces the risk of human injury or self-injury.

What are the circumstances where a simple punishment should help to correct aggressive behavior?

None. Research shows us that punishment is likely to increase fear, anxiety, and aggression.


Christine D. Calder, DVM, DACVB

Source: From Cohn and Côté: Clinical Veterinary Advisor, 4th edition. Copyright © 2020 by Elsevier Inc. All rights reserved

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