Small animal - February 2025

The International Association for the Study of Pain (IASP) defines pain as “an unpleasant sensory and emotional experience typically caused by, or resembling that caused by, actual or potential tissue injury”. This definition highlights that pain involves both physical sensations and emotional distress, making it an important factor to consider in behavioural assessments and treatment.

Pain is frequently overlooked as a contributing factor in canine behavioural problems, despite its profound prevalence and impact. Professor Daniel Mills, a leading veterinary researcher and behaviourist at the University of Lincoln, emphasises that many behavioural issues in dogs are either directly linked to, or exacerbated by, physical pain. Effective management of this pain often leads to a significant reduction or in many cases complete resolution of associated behavioural problems. There is a tendency to view behaviour problems as distinct from medical issues. Behavioural changes are often the first, and sometimes the only, indication of an underlying medical problem, including pain (Denenberg, 2018).

Professor Mills’ analysis of clinical cases revealed a striking prevalence of pain-related behavioural issues, with rates ranging from 28 per cent to 82 per cent depending on the population studied. These findings underscore the necessity of vigilant observation, as pain-related conditions often manifest subtly through changes in a dog’s behaviour. Importantly, this issue is not confined to aging dogs. Osteoarthritis, for instance, affects approximately 20 per cent of dogs older than one year (Mills et al, 2020) and when pain is identified as the cause of aggressive behaviour, the data from Beaver (1983) indicates an excellent prognosis, with all cases in the review achieving successful treatment outcomes (Barcelos et al, 2015). A 2012 study focusing on aggressive dogs with a pain component found that musculoskeletal pain, particularly from hip dysplasia and elbow osteoarthritis, was the primary cause in 75 per cent of the cases (nine out of 12) (Camps et al, 2012).

Common areas where dogs experience pain include:

• joints – hips, knees, wrists/ankles, spine, shoulders, and elbows;
• ears – chronic infections or inflammation;
• dental issues – tooth pain or gum disease (including retained deciduous teeth);
• gastrointestinal problems – stomach or intestinal discomfort (including diarrhoea);
• dermatological conditions – persistent skin irritation or inflammation.

How pain contributes to problem behaviours

Pain can contribute to problematic behaviours in several ways, either as a direct cause or by exacerbating existing issues:

1. Pain as a direct cause of behavioural problems

Dogs in pain may display protective behaviours such as aggression or avoidance to minimise further discomfort. For example, a dog with hip dysplasia or angular limb deformities may growl or snap when handled due to underlying pain (Mills & Zulch, 2023).

2. Pain amplifying existing behaviours

Pain can lower a dog’s overall threshold for aggression and may trigger specific aggressive behaviours as part of a defensive or protective response (Landsberg et al. 2013).

Chronic pain can intensify behavioural issues, leading to distinct patterns such as:

increased impulsivity: the dog may react without typical restraint;

generalisation: aggressive behaviours may extend to broader contexts;

physical signs: dogs with musculoskeletal pain may exhibit “easily broken up” attacks or a tendency to bite extremities like hands or feet.

3. Anxiety and avoidance

Dogs in pain may become more anxious or avoidant as they attempt to shield themselves from situations or actions that might exacerbate their discomfort. For example, a dog with joint pain may avoid car travel, stop on walks, avoid stairs or certain movements.

4. Lowered resilience

Chronic pain places a psychological and physiological burden on dogs, reducing their ability to cope with other stressors. This can result in irritability, increased susceptibility to minor illnesses, or behavioural changes.

5. Attention-seeking behaviour

Dogs may become clingier when in pain, seeking comfort and social support.

Signs of pain in behaviour

Pain often reveals itself through various behaviours that can act as important indicators of underlying discomfort. In a 2023 paper, Professor Daniel Mills and Dr. Helen Zulch compiled a detailed table highlighting behavioural issues and their potential medical causes. Key behavioural indicators of pain and discomfort include:

Mobility issues: reluctance to move, hesitation to sit, or a lazy sitting position, stiffness, lameness, difficulty jumping, an unusual gait, or reluctance to walk on slippery surfaces. Additionally, a dog may display out-of-context behaviours such as lip-licking or yawning while transitioning in and out of positions;

Comfort-seeking: increased clinginess or dependence on human companions;

Changes in appetite: increased or decreased eating habits, consuming non-food items (PICA) in non-teething adult dogs, and resource guarding;

Touch sensitivity: snapping or biting when handled, often indicating pain from touch or movement;

Self-directed behaviours: excessive chewing, licking, or biting of specific areas, particularly in dogs beyond the teething stage;

Heightened anxiety: sudden changes in behaviour, heightened sensitivity to noises, or unexpected episodes of panting;

Sudden aggression/reactivity: this includes growling, air snapping, or biting that appears unexpectedly;

Hyperarousal or hyperactivity: excessively intense behaviours that seem over the top compared to typical excitement or activity levels;

Excessive mouthing: intense and persistent mouthing that exceeds typical play behaviour – bruising may be present, but there are no puncture wounds;

Intense vocalisation: unusually frequent or intense barking, howling, or other vocalisations;

Restlessness: the dog may seem unable to settle down, may be constantly moving, or may engage in intense humping, particularly around moments of excitement;

Altered sleep patterns: sleeping significantly more or less than expected for the dog’s age. Often seeking out unusually hard or cold places for resting;

Disturbed routine patterns: unusual toileting behaviours or excessive elimination. A dog who had been but is no longer house trained;

Compulsive behaviours: guarding specific areas or items excessively, pacing, digging, or repeatedly engaging in other intense seeking or stealing behaviours;

New behaviours: behavioural changes emerging after the age of one, with no prior history, such as pulling on the lead, guarding food or objects, increased reactivity, excessive barking, and similar behaviours.

Barriers to recognising pain in dogs

Identifying pain in dogs presents numerous challenges, starting with the reliance on owners to recognise and report signs. Veterinarians can only assess and treat pain when dogs are brought to the clinic, making the owner’s ability to detect behavioural changes critical. Owners often observe subtle shifts, such as changes in activity levels or temperament, and must decide whether these warrant a veterinary visit. However, even with this input, veterinarians depend on the owner’s knowledge of their dog’s normal behaviour and their ability to communicate these changes effectively. Additionally, there are no standardised methods currently available to use behaviour as a tool for diagnosing pain in dogs (Parker, 2024).

Subtlety of pain indicators

Pain in dogs does not always present as obvious signs like yelping or limping. Mild symptoms, such as stiffness, reluctance to engage in activities, or subtle changes in gait, may be overlooked or dismissed. Compounding the difficulty, some dogs may continue participating in high-energy activities, like ball-chasing, even when in pain. Aerobic exercise triggers the release of endorphins, which are natural pain relievers, helping to reduce the perception of pain. Exercise has been shown to provide pain relief (analgesia) for conditions such as low back pain, osteoarthritis, myofascial pain, chronic fatigue syndrome, and fibromyalgia (Bement & Sluka, 2016).

Challenges in the veterinary clinic

Assessing chronic pain during a typical clinic visit is especially challenging. The veterinary clinic environment is unfamiliar and often stressful for dogs, triggering a heightened stress response. This stress releases adrenaline, which can temporarily numb pain, making the dog appear more mobile and less uncomfortable. Anxiety may also alter the dog’s behaviour, causing agitation or withdrawal that can obscure pain-related signs (Covey-Crump, 2018).

Chronic pain often manifests in specific contexts, such as difficulty navigating stairs, avoiding certain movements, or struggling with routine activities like eating, resting or even eliminating. These behaviours are difficult to replicate in the clinic, where the dog is unlikely to engage in its usual activities. Furthermore, static examinations rarely reveal pain that only becomes evident during specific movements, such as walking, sitting, or jumping on and off furniture.

Time constraints and fluctuating pain

A typical veterinary appointment is too brief to capture the full scope of a chronic pain condition. Pain levels can fluctuate based on factors like activity, time of day, or weather, making a single visit insufficient for a comprehensive assessment. Dogs experiencing intermittent or low-grade chronic pain may appear relatively normal during a short examination, especially if they are having a “good day.”

Masking pain and stoic breeds

Stress, excitement, or high-energy activities can release endorphins, natural painkillers that temporarily reduce pain perception. This effect is particularly pronounced if the dog has been stressed during the journey to the clinic. Certain breeds or individual dogs may also exhibit stoic tendencies, suppressing signs of pain as a survival mechanism. Subtle indicators like stiffness or reluctance to jump may go unnoticed or be dismissed (Caddiell et al, 2023) and some conditions, such as patellar luxation, are sometimes mistakenly believed to be painless.

However, research has demonstrated that medial patellar luxation (MPL) can lead to cartilage erosion, causing significant joint pain and dysfunction in affected dogs (Kim et al, 2024).

Long-standing pain and learned behaviours

Dogs with chronic pain often adapt to their discomfort over time, altering their behaviour in ways that can be mistaken for aging or temperament changes. For example, a dog may become more passive or withdrawn due to persistent low-grade pain. Additionally, some dogs develop learned responses to pain, such as avoiding certain movements or activities. These responses can persist even after the pain is alleviated, complicating the assessment process.

Limitations of clinical observation

Dogs cannot verbally communicate their pain, and pain assessment relies heavily on subjective behavioural indicators, which vary widely between individuals. The clinical environment often fails to elicit the same behavioural responses seen in the dog’s home or during daily activities. Chronic pain conditions like osteoarthritis or soft tissue injuries may only become apparent during specific movements or sustained activity, which are not typically observed during a brief clinic visit.

Risk of misdiagnosis

Pain-related behaviours, such as irritability, restlessness, or reluctance to move, can easily be misinterpreted as anxiety, fear, or normal aging. Without a clear connection to physical discomfort, these behaviours may be overlooked or misdiagnosed, delaying appropriate treatment. Accurately assessing chronic pain in dogs requires a nuanced approach that goes beyond a standard clinic visit. Recognising the challenges of pain assessment is critical to ensuring timely and effective treatment. If pain is suspected a comprehensive pain trial should be carried out.

What is a pain trial and why is it important?

Running a pain trial in dogs is crucial for accurately diagnosing and managing pain-related behavioural changes. It is recommended that a pain trial should last 6–8 weeks. This enables veterinarians to evaluate the effectiveness of analgesic treatments by monitoring behavioural and physical responses over time (Mills et al, 2020). This extended approach is essential because short-term assessments often fail to detect the subtle or fluctuating effects of chronic pain. Despite their importance, short-term pain trials are more commonly conducted, leading to the critical question: why are they often insufficient?

Delayed onset of therapeutic effects: many analgesic medications, especially those addressing chronic pain (e.g., NSAIDs, gabapentin), take time to exert their full effects. Short trials may not allow sufficient time to observe the cumulative effects of these treatments.

Adaptation of pain pathways: chronic pain often leads to changes in the central and peripheral nervous systems, such as sensitisation (e.g., allodynia or hyperalgesia). These adaptations may take weeks to “reset” or reduce in response to appropriate analgesic treatment. A short trial does not provide enough time to address these maladaptive processes (Volcheck et al, 2023).

Behavioural habituation: pain-induced behaviours can become learned or habitual, even after the initial pain subsides. A dog with joint pain may have developed avoidance behaviours, such as noise sensitivity (Lopes Fagundes et al, 2018). These behaviours may persist even after pain reduction, as the dog may need time to relearn and trust pain-free movement. Short trials may not capture this behavioural adaptation process, leading to the false conclusion that the pain persists.

Intermittent or subtle pain expression: dogs experiencing intermittent or low-grade chronic pain may not exhibit overt behavioural changes during a brief observation period. Pain symptoms may fluctuate depending on activity levels or environmental factors. Behavioural signs like restlessness or reluctance to perform certain tasks may require sustained observation to detect improvement. Short trials can miss these nuanced changes.

Cumulative effects of chronic pain: chronic pain can lead to systemic and emotional changes. Anxiety or irritability, which may take longer to resolve than the pain itself. Muscle atrophy or changes in gait from prolonged compensatory behaviours, which may require rehabilitation in addition to pain management. A longer trial allows these secondary effects to improve, providing a more accurate picture of the treatment’s effectiveness (Goldberg, 2024).

Overcoming barriers with a multidisciplinary approach

A diagnosis of “behavioural” is never a final answer but rather a starting point for deeper investigation. Behavioural issues always have a trigger, whether it’s environmental, physiological, or a combination of both. Behavioural problems, such as aggression, are often mistakenly attributed to a dog’s attempt to assert dominance over their caregiver. However, the “alpha dog” or “leader of the pack” theory has been widely debunked (Bradshaw et al 2016). Applying this outdated concept to domestic dogs is not only misguided but also potentially harmful. The belief in the need to dominate or establish oneself as the “alpha” can result in inappropriate training methods, such as physical punishment or intimidation. These methods often exacerbate fear, anxiety, or aggression in dogs and may lead to the misdiagnosis of underlying medical conditions. Pain, in particular, is a common but frequently overlooked contributor to behavioural issues, underscoring the need for a more compassionate and science-based approach to understanding and addressing canine behaviour.

Labelling a dog’s aggression, anxiety, or hyperactivity as “behavioural” without exploring potential medical causes does a disservice to both the dog and the owner. This underscores the importance of integrating behaviour assessments into veterinary practice.

Pain-related behavioural issues often require collaboration between veterinarians, behaviourists, and physiotherapists:

• veterinarians: diagnose and manage medical aspects of pain;
• behaviourists: identify and address behaviour changes linked to discomfort; and,
• physiotherapists: perform gait analyses and develop rehabilitation plans.

Collaboration between veterinarians, qualified animal behaviourists, and physiotherapists is essential when diagnosing the link between pain and behavioural changes in dogs. Veterinarians play a key role in identifying and managing medical causes of pain, while behaviourists can assess how pain manifests in a dog’s actions and emotional responses. Physiotherapists contribute by evaluating movement, gait, and physical limitations that may indicate discomfort.

Alternative therapies, such as hydrotherapy, acupuncture, and other holistic treatments provided by veterinary professionals, can also be valuable options to consider. By working together, these professionals can provide a holistic approach to diagnosis and treatment, ensuring a more accurate understanding of the pain-behaviour link and ultimately improving the dog’s quality of life.

Conclusion

Pain is a significant, yet frequently overlooked, contributor to behavioural problems in dogs. By understanding its subtle manifestations and addressing barriers to recognition, veterinarians can improve diagnostic accuracy and outcomes. Pain trials and collaborative care are essential tools for identifying and managing pain, ensuring better quality of life for dogs and their owners. Recognising the impact of pain is not just about alleviating discomfort — it’s about restoring the physical, emotional, and behavioural health of our canine companions.

As Dr. Debbie Gross Torraca, a veterinarian and board-certified orthopaedic clinical specialist, advises: “Assume it is pain, until proven otherwise.”