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Small Animal

Small animal - April 2024

Aggressive behaviour in dogs

Dog trainer Suzi Walsh BSc MSc discusses dog aggression and how to handle an aggressive dog in a veterinary clinic

Clients typically first turn to their veterinary practice for help and advice when they are concerned about their dog’s aggressive behaviour. Dog aggression is a huge problem and refers to any behaviour displayed by a dog that is intended to cause harm or threat to another animal or person. This behaviour can manifest in various forms, including growling, barking, lunging, snarling, or even biting. Aggression in dogs can be directed towards other dogs, animals, humans and even objects. However, aggressive behaviour is mainly a defensive mechanism used to increase space between the dog itself and the stimulus. In its simplest form, aggression is a manifestation of fear, frustration or undiagnosed pain/discomfort. Understanding the underlying cause of a dog’s aggression is crucial for implementing effective behaviour modification and ensuring the safety and well-being of the dog and those around them.

Aggressive behaviour in dogs is often misunderstood as dominance. The concept of dominance theory, particularly as it pertains to dog behaviour, has been largely debunked by modern research in animal behaviour science. Dominance theory originated from studies of captive wolf packs in the mid-20th century, but subsequent research on wild wolf behaviour and observations of domestic dog behaviour have challenged and revised many of the original conclusions (Bradshaw et al, 2016).

Studies have shown that wolf pack dynamics are more complex and cooperative than previously believed, with relationships based more on familial bonds and cooperation than dominance hierarchies. Furthermore, attempts to apply wolf pack behaviour directly to domestic dogs have been found to be inaccurate, as dogs have different social structures and behaviours shaped by their domestication history and living environments.

Modern approaches to understanding and addressing dog behaviour emphasise positive reinforcement training, understanding individual motivations and emotions, and promoting cooperative relationships between dogs and humans. This approach focuses on building trust, communication, and mutual respect rather than relying on outdated notions of dominance and submission.

In addition, mistreatment and abuse can create triggers that may lead to aggressive behaviour in dogs. Similarly training, both deliberate or through incompetence, can create an aggressive dog. Misinformation provided to dog owners from unqualified pet professionals or members of the public advising the need to physically correct a dog for ‘bad’ behaviour and other forms of neglect can often lead to a dog biting.

Aggressive body language

Aggressive dog body language can vary depending on the individual dog and the context, but some common signs to watch for include:

Avoidance behaviour: Body language like lip licking, panting, yawning, a paw raise, avoiding eye contact and touch, can all be signs a dog is uncomfortable. Ignoring these can result in an escalation to aggressive behaviour.

Stiff or tense body posture: An aggressive dog may stand stiffly or rigidly, with their body tense and muscles visibly contracted.

Raised hackles: The hair along the dog’s back may stand up (hackles raised), indicating heightened arousal or aggression.

Direct staring: Aggressive dogs may maintain a fixed, intense stare, often accompanied by a furrowed brow or narrowed eyes.

Growling or snarling: Vocalisations such as growling, snarling, or barking aggressively are clear indicators of aggressive behaviour.

Bared teeth: An aggressive dog may curl their lips back to expose their teeth in a threatening display.

Raised lips: Lips pulled back and raised may signal aggression, especially when accompanied by bared teeth or growling.

Wrinkled muzzle or forehead: Wrinkles or furrows on the dog’s muzzle or forehead may indicate tension or aggression.

Lunging or charging forward: Aggressive dogs may lunge forward or charge at perceived threats, often with their body held low to the ground in a predatory stance.

Stiff tail or wagging held high: While a wagging tail is typically associated with happiness or excitement, a stiff tail held high can indicate aggression or agitation.

Freezing or stillness: In some cases, aggressive dogs may freeze in place, becoming completely still as they assess the situation before potentially escalating their behaviour.

It’s essential to recognise these signs of aggression and respond appropriately to prevent escalation and ensure the safety of both the dog and others nearby. If you observe these behaviours in a dog, it’s best to give them space and avoid provoking or approaching them until the situation can be assessed and managed safely.

Causes of dog aggression

Fear and anxiety

Dogs may become aggressive when they feel threatened or frightened. This can happen due to past traumatic experiences, lack of socialisation, or genetic predisposition. Some of the ways that dogs exhibit fear aggression are in territorial behaviour, and possessive behaviour, as well as reactivity to vehicles, noise, humans and other animals, including other dogs and unfamiliar environments.

Socialisation before vaccines are completed

Nervous dogs are primarily a result of inadequate socialisation in dogs. It’s crucial for puppies to be nurtured in a home setting, receiving consistent and gentle handling starting around three weeks old. They should be exposed to various stimuli typical of a household environment. Affection from humans and social interaction are essential for them to develop into confident, well-adjusted companions by the time they reach 12 to 14 weeks old, enabling them to thrive in a human-centric world.

Dr Frank McMillan, an expert in animal welfare and canine trauma, conducted research on the lasting impacts of commercially raising puppies. The prevailing outcome across various studies he reviewed indicates a notable rise in aggressive behaviour.

About a week after a puppy’s initial round of vaccines is a suitable time to begin introducing them to safe socialisation activities (Howell et al, 2015). These activities don’t necessarily involve direct contact with other dogs – indeed, it’s best to avoid such interactions. The only exception is interacting with dogs known to be healthy and vaccinated.

There are various ways to expose a puppy to different environments while minimising the risk of illness. Here are some options:

  • Carry a puppy while exploring new places such as with a specially-designed backpack or sling.
  • Set up a fully-enclosed, pop-up, portable puppy pen, providing a safe space for a puppy at parks or beaches. Consider bringing along a potty pad for their convenience.
  • Bring the puppy on a drive and park the car in different locations and sit with a puppy inside, observing the surroundings. Start with closed windows to focus on sights, then gradually open windows to introduce sounds and smells.
  • Try to offer small treats when they spot something new, such as a small child, or if they hear a loud noise. This helps to create a positive association between the new experience and something a puppy enjoys (the treat).

If a puppy shows signs of tension, barking, fear, or stress, immediately increase distance or decrease intensity to provide them with space to process. If the situation becomes overwhelming, leave the area and try again later.

Pain and discomfort

While some concerns regarding dog behaviour may stem from emotional factors like anxiety, it’s important to recognise that a significant portion of cases may have underlying medical conditions contributing to, or causing, these issues. Research indicates that up to 80 per cent of cases seen by behavioural clinicians involve some degree of medical involvement. Musculoskeletal issues are frequently cited, but there’s also growing awareness of the significance of gastrointestinal, testicular, dental and dermatological issues, which might initially present as symptoms of anxiety in the animal (Mills et al, 2023). It’s important to recognise that the personality of an animal isn’t the sole cause or rationale behind their behaviour; rather, it serves as a risk factor. Therefore, problem issues should not be disregarded as an assumption of poor temperament.

Signs that there is a medical reason for a behavioural issue:

  1. Abrupt behavioural change.
  2. More than one new change in behaviour.
  3. Rapid progression of the behavioural issue.
  4. The animal is exhibiting an unusual gait or posture regardless of the breed.
  5. A surprising degree of generalisation.
  6. A Jekyll and Hyde personality.
  7. Relationship between the change in behaviour and physical exercise.
  8. Coincidental onset when a dog starts treatment for an unrelated medical issue.
  9. Unusual age, a new behaviour for an adult animal with no previous history of an issue.
  10. Failure of behaviour modification programme by a qualified behaviourist.
  11. Pica can be associated with GI issues or even musculoskeletal pain.
  12. Compulsive behaviour is an under-recognised manifestation of gastro-intestinal pain.

If a dog presents with one or more of these signs, they should be considered as candidates for a further investigation or a pain trial (Mills et al, 2020).

Limitations of veterinary clinic

Assessing chronic pain in a veterinary clinic can be a hard task as nearly everything that is carried out during an examination is going to be stressful for the animal. This, coupled with very short consultation times and the impossibility of communicating with the patient, makes veterinary work more challenging than other medical professions. Other limitations include:

Subjectivity: Pain assessment in animals relies heavily on subjective observations and interpretations, as animals cannot directly communicate their pain experience. Veterinarians must rely on behavioural cues, body language, and owner-reported signs, which can be influenced by individual interpretation and bias.

Masking behaviours: Animals, especially prey species, have evolved to mask signs of pain as a survival mechanism. This can make it challenging to accurately assess chronic pain, as animals may exhibit subtle or inconsistent signs, or they may display compensatory behaviours that mask their discomfort. A dog who is stressed might release high levels of adrenaline and cortisol which may make diagnosing pain quite difficult.

Breed variability: Different breeds of dog have unique pain responses and expressions, making it difficult to generalise pain assessment techniques across all animals. What may be considered a reliable indicator of pain in one species may not hold true for another. Certain breeds of dogs also tolerate more pain than others or don’t express discomfort in the same manner.

Multimodal nature of pain: Chronic pain often involves multiple underlying causes and manifestations, making it complex to assess comprehensively in a clinical setting. Pain may present differently depending on its origin (e.g., musculoskeletal, neuropathic, or visceral), which requires a multifaceted approach to evaluation.

Owner compliance: Owners’ ability to recognise and report signs of chronic pain in their pets can vary widely, affecting the accuracy of pain assessment. Additionally, owner compliance with treatment plans and follow-up assessments may impact the veterinarian’s ability to monitor and manage chronic pain effectively.

Lack of standardisation: Despite efforts to develop standardised pain assessment tools for animals, there is still a lack of universal consensus on the most reliable and valid methods for assessing chronic pain. This can lead to variability in assessment techniques and interpretations across veterinary clinics and practitioners.

Diagnostic challenges: Identifying the underlying cause of chronic pain can be challenging, requiring diagnostic tests such as imaging, laboratory tests, and specialist consultations. However, these diagnostic procedures may not always be feasible or accessible in a primary care veterinary clinic setting.

Despite these limitations, veterinarians continue to refine pain assessment techniques and develop innovative approaches to better recognise and manage chronic pain in animals. Collaborative efforts between veterinarians, researchers, and animal caregivers are essential for advancing our understanding of chronic pain and improving pain management strategies in veterinary medicine.

Handling an aggressive dog

Handling an aggressive dog in a veterinary clinic requires a combination of safety measures, understanding of the dog’s behaviour, and appropriate techniques to minimise stress and potential harm to both the dog and veterinary staff. Here are some steps to handle an aggressive dog in a veterinary clinic:

Safety first: The safety of all individuals involved should be the top priority. Ensure that veterinary staff are trained in handling aggressive dogs and have access to necessary safety equipment, such as muzzles, gloves, and safety restraints.

Assess the situation: Evaluate the dog’s behaviour and level of aggression to determine the best approach. Consider factors such as how urgent the care is at that moment in time, the dog’s body language, vocalisations, how much discomfort the dog may be experiencing and past behaviour. If possible, reschedule the appointment to an alternative time and speak to the client about muzzle training or engaging with a qualified dog trainer or behaviourist.

Create a calm environment: Minimise stressors in the environment by reducing noise, distractions, and crowding. Keep the dog separated from other animals and provide a quiet, controlled area for assessment and treatment.

Use positive reinforcement: Employ techniques such as desensitisation, counterconditioning, and reward-based training to encourage calm and cooperative behaviour in the dog. Offer treats, praise, and gentle handling to create positive associations with veterinary visits.

Avoid provocation: Avoid actions or stimuli that may trigger or escalate the dog’s aggression, such as sudden movements, prolonged eye contact, or restraining techniques that increase stress.

Maintain distance: Maintain a safe distance from the dog and use barriers or restraints to prevent bites or attacks. Consider sedation or anaesthesia, if necessary for the safety of the dog and veterinary staff.

Document behaviour: Keep detailed records of the dog’s behaviour, responses to handling techniques, and any incidents of aggression for future reference and treatment planning.

Ensure follow-up care: Schedule follow-up appointments to monitor the dog’s progress, adjust treatment strategies as needed, and provide ongoing support for the dog and their owner.

Handling aggressive dogs in a veterinary clinic requires patience, skill, and a compassionate approach to ensure the safety and well-being of all involved. By implementing appropriate safety measures, understanding the dog’s behaviour, and using positive reinforcement techniques, veterinary staff can effectively manage aggressive behaviour and provide necessary care for the dog.

When is a muzzle appropriate?

Muzzles can be crucial tools, especially if a dog is trained to use one. However, introducing a muzzle to a dog who has never worn one before can potentially lead to future challenges. If a dog links wearing a muzzle with unpleasant experiences, like trips to the vet, it could create lasting negative associations that impact their well-being and future visits.

Muzzles can induce fear and stress in dogs, especially if they are not accustomed to wearing them. This can escalate their anxiety during veterinary visits, potentially leading to aggressive behaviour or further distress.

Muzzles restrict a dog’s ability to communicate with their owner and the veterinary staff. They may not be able to vocalise signs of distress or discomfort, making it challenging to address their needs effectively.

Muzzling a dog can mask symptoms of fear, pain, or illness, making it difficult for veterinarians to accurately assess their condition. This could result in missed diagnoses or delayed treatment.

Instead of relying solely on muzzles, veterinary clinics can employ alternative strategies such as positive reinforcement training, desensitisation, and counterconditioning to help dogs feel more comfortable and cooperative during exams and procedures. These approaches not only reduce stress and anxiety for the dog but also promote a positive veterinary experience for all involved.

Begin implementing these strategies early in a dog’s life, ideally during puppyhood. Consider hosting puppy parties or puppy classes at your veterinary clinic to foster positive experiences and associations with visiting. This approach helps create a dog that loves visiting a veterinary clinic.

Muzzles are a necessary part of animal husbandry, however it’s important to assess what care is urgent and what can be delayed until the client has time to muzzle-train their dog.

A wonderful resource for veterinary clinics and clients is the which has some terrific posters and flyers encouraging safe muzzle use.

Cooperative care

Cooperative care for dogs involves a collaborative approach between the dog and their owner or caregiver during grooming, veterinary care, and other medical procedures. Instead of using force or restraint, cooperative care focuses on building trust and cooperation through positive reinforcement training techniques. This may include teaching the dog to willingly participate in activities such as nail trimming, ear cleaning, vaccinations, and veterinary examinations. The goal is to create a stress-free and positive experience for the dog, leading to better overall well-being and a stronger bond between the dog and their caregiver. Forcefully restraining a dog can lead to consequences such as fear of strangers and issues with future handling.

Cooperative care has been used for many years both in laboratory and zoo animals in order to make animal husbandry easy and stress-free. Imagine manoeuvring a sea lion with force for medical checks or simply administering eye drops.

Cooperative care in a veterinary clinic for giving eye drops involves training the dog to voluntarily participate in the process. Here’s an example:

Desensitisation: Start by desensitising the dog to the sight and feel of the eye dropper. Show the dropper to the dog and offer treats or praise to create a positive association.

Counterconditioning: Pair the eye dropper with treats or other rewards to create a positive association with the eye drop procedure. For example, offer a treat immediately after showing the dropper.

Touch conditioning: Gradually introduce touch around the dog’s eyes and eyelids to get them comfortable with the sensation. Use a gentle touch and offer rewards for calm behaviour.

Mock application: Practise the motion of applying eye drops without actually administering any liquid. Reward the dog for remaining calm and cooperative during this simulation.

Gradual introduction of eye drops: Once the dog is comfortable with the previous steps, introduce a saline solution or lubricating eye drops to the eye dropper. Begin by applying a small amount near the corner of the eye without directly touching the eye.

Reinforcement and gradual progress: Offer treats and praise for each successful step of the process. Gradually work up to applying the eye drops directly into the eye, rewarding the dog for remaining calm and cooperative throughout.

Consistency and patience: Consistently practise the cooperative care routine with the dog to reinforce positive behaviour and ensure they remain comfortable with the procedure over time. Be patient and go at the dog’s pace to avoid causing stress or discomfort.

By using positive reinforcement training techniques and gradually introducing the eye drop procedure, the dog learns to associate it with positive experiences, making future administrations easier and less stressful for both the dog and veterinary staff. A great resource for a fear-free clinic is with practical information for staff and clients.

Mental health of vet

Veterinarians, like all healthcare professionals, can experience stress and emotional strain when working with aggressive animals. Dealing with aggressive dogs can be physically and emotionally demanding, leading to burnout, compassion fatigue, and even secondary traumatic stress. It’s crucial for veterinarians, veterinary nurses and veterinary technicians to prioritise their mental health and seek support when needed. This may involve peer support networks, counselling services, and training in stress management techniques. Additionally, creating a supportive work environment and implementing safety protocols can help mitigate the risks associated with working with aggressive animals.

Help from qualified behaviourist

Seeking assistance from qualified behaviourists or trainers is a proactive step for veterinary professionals when dealing with aggressive dogs. Behaviourists and trainers can provide expertise in understanding and addressing the underlying causes of aggression in dogs, as well as effective techniques for managing and modifying behaviour.

Collaboration between veterinary professionals and behaviourists/trainers can lead to better outcomes for both the animals and the professionals involved. It’s important for veterinary professionals to recognise when they need additional support and to leverage the expertise of other professionals in the field.


Bradshaw JWS, Blackwell EJ, Casey RA. (2009): Dominance in domestic dogs—useful construct or bad habit? J Vet Behaviour. 2009 May-June 4(3) 135-144. 

Bradshaw JWS, Blackwell EJ, Casey RA. (2016): Dominance in domestic dogs – A response to Schilder et al. (2014) J Vet Behaviour. 2016 Jan-Feb Vol.11 102-108.

McMillian FD, Serpell JA, Duffy DL, Masaoud E, Dohoo IR. (2013): Differences in behavioral characteristics between dogs obtained as puppies from pet stores and those obtained from noncommercial breeders. J Am Vet Med Assoc. 2013 May 242(10): 1359-63.

Howell TJ, King T, Bennett TC. (2015) Puppy parties and beyond: the role of early age socialization practices on adult dog behavior, Veterinary Medicine: Research and Reports, 6: 143-153.

Mills DS, Demontigny-Bédard I, Gruen M, Klinck MP, McPeake KJ, Barcelos AM, Hewison L, Van Haevermaet H, Denenberg S, Hauser H, Koch C, Ballantyne K, Wilson C, Mathkari CV, Pounder J, Garcia E, Darder P, Fatjó J, Levine E. Pain and Problem Behavior in Cats and Dogs. Animals (Basel). 2020 Feb 18;10(2):318. 

Mills, D. and Zulch, H. (2023), Veterinary assessment of behaviour cases in cats and dogs. In Practice, 45: 444-458. 

Book: Canine Behavior: A Photo Illustrated Handbook by Barbara Handelman (2008-06-01).

Readers questions and answers

1. A dog snarls and snaps at you with its ears flat against its head, its hackles raised, and its tail tucked tightly against its rear. What kind of aggression does this dog have?

A: The dog is not being aggressive 

B: Dominance aggression

C: Fearful aggression

D: Territorial aggression

2. What is not a likely behavioural sign that a dog might be in some discomfort? 

A: Jumping on guests

B: Eating socks

C: Sudden reluctance to walk

D: Obsessive licking

3. What is the primary reason that socialisation is vitally important?

A: Making the adult dog more intelligent

B: Preventing a puppy from nipping and mouthing

C: Preventing fears in adult dogs

D: Teaching a puppy how to greet people nicely

4. When should you opt to use a muzzle?

The treatment a dog requires is urgent and the dog cannot be sedated

A: A muzzle should be used on every dog

B: A muzzle should only be used on restricted breeds

D: A muzzle should only be used if a dog has a bite history

5. Cooperative care is best described as:

A: Restraining a dog until it cooperates

B: Trained behaviours that allow for a mutual partnership between the care team and the animal

C: Waiting until the dog submits in order to carry out a procedure

D: Tricking the dog into accepting veterinary care

Answers: 1C; 2A; 3C; 4A; 5B.