The relationship between pain and aggression in dogs

How experiencing physical pain can negatively impact a dog’s behaviour.

Aggression can be defined as behaviour perceived as threatening which is intended to cause harm or to increase distance from the recipient. Aggressive responses can be used to communicate these intentions through body posturing, facial expressions as well as vocalisations. Overtly aggressive responses can include but are not restricted to

·      Biting

·      Snapping

·      Lunging

·      Growling

·      Snarling

·      The baring of teeth

·      Hard stares and

·      Rigid body posture.

Often there are many precursors to an aggressive response such as stress and/or fear behaviours shown in more subtle signalling and often avoidance strategies will be attempted before a dog resorts to an aggressive display or response. All dogs, when feeling sufficiently threatened, are capable of demonstrating a spectrum of aggressive responses and behaviours. Many factors will influence every single dog’s behaviour in specific situations. Every dog will have their own individual aggression threshold which will be affected in varying degrees by the following factors

·      Genetic predisposition

·      Prenatal and socialisation period environments.

Other factors can also add to a situation such as

·      Noises

·      Familiarity to the individual and whether pain is indeed a factor.

Painful medical conditions can often lead to irritability and then in turn decrease the dog’s threshold for aggression.

It is widely acknowledged that pain is a potential factor in many problematic behaviours although reporting such links has been lacking and conclusive evidence is hard to present due to the individuality of the dogs and the problem behaviours they might display. The relationship between aggressive responses and pain can be complex and varied. Behaviour changes are the most common indicator of pain and can be demonstrated as ‘lost normal behaviours’ such as decreased movement and/or appetite or as ‘developed abnormal behaviours’ of which the most common are aggressive responses.

One of the fundamental factors in working with a dog with aggressive behavioural issues is to first rule out any underlying medical conditions or pain that the dog may be experiencing as behaviour modification will simply not work if the dog is suffering physically. Often what is thought to initially be a problem behaviour is actually an indicator of something else going on in that dog’s body. This is one of the main reasons why most of us who work within the profession of dog behaviour and training recommend (or insist) on a full veterinarian check up prior to undertaking any behaviour work to rule out undiagnosed conditions that may be influencing a dog’s behaviour.

Organ dysfunction such as liver or kidney, neurological diseases and hormonal disorders (adrenal, thyroid or sex glands) can lead to pain aggression. If a condition is undiagnosed then no matter how great a behavioural modification programme may appear, it will not work for that dog unless any pain is treated first.

Pain can also exacerbate any anxiety or fear that a dog may be experiencing. Unfortunately for the sufferer, these emotions can be either from experiencing the pain itself (or from an outside influence) but this is a vicious circle as the physical responses to any fears, anxiety or stress stemming from the experience of the pain can in themselves cause more pain. Muscle tension or trembling could cause more intense pain which then increases the fear or anxiety that dog is feeling. If the dog has experienced pain within a specific context, they may try to avoid even remotely similar contexts in the future, displaying reactive responses even when actual pain is not yet being experienced.

Dr Daniel Mills FRCVS, a veterinary researcher and behaviourist from the University of Lincoln submits that a large percentage of behavioural problems are caused by or exacerbated by pain, and that by resolving the pain could mitigate or even stop the problematic behaviours. Dr Mills went on to collaborate with other behaviourists and researchers to create a unique framework to help assist others when considering pain influenced behaviour cases. The framework consists of four categories. Please note it is a very in depth framework however I am only focusing on the points relating to aggressive responses

·      Unwanted problematic behaviour caused by pain including fear, anxiety, aggression, resource guarding.

·      Pain causing secondary behavioural issues in addition to existing ones

·      Unwanted behaviour exacerbated by pain such as tensing from anxiety causing musculoskeletal pain to increase

·      Behaviours that potentially are not problematic to the owners but are indicative of pain being experienced

Behaviour caused as a direct manifestation of pain

Some clear indications of pain are

·      Limping

·      Flinching

·      Yelping

·      Licking the area of concern

These are obvious to owners and veterinarians while some other manifestations of pain are much less recognisable including those behaviours considered undesirable such as aggressive responses. Dogs displaying pain based aggression are likely to display sudden and unexpected changes in their behaviour as if they have developed a split personality. These aggressive behaviours are most commonly encountered if the dog is directly approached by someone, particularly if the dog is lying down. Dogs in severe pain are often reluctant to move on command or request. These episodes of aggression are typically brief and easier to interrupt and will usually target a limb extremity of the person approaching them. Often these bite incidents are classified as a lower level violent threat and are done as an attempt to prevent any further interaction with the dog. It is also highly probable that previous, more subtle warning signals could have been ignored causing the dog to escalate their aggression. This can make these incidents appear to occur without warning or ‘out of the blue’. Dogs who previously were not deemed to be aggressive prior to the onset of pain could appear more impulsive than before the onset of pain but dogs who had already displayed aggressive responses before could appear less impulsive but more frequent and intense in their displays of aggressive responses. One study showed that younger dogs were more likely to demonstrate these behaviours as they were still learning how effective certain behaviours could be whereas older dogs may learn to supress these signals through their previous learning history. 

Pain causing secondary behavioural issues

In some cases, training progress can slow or stop and the final steps can be elusive due to an undiagnosed pain issue. Sometimes what can appear to be a behaviour caused by a separate issue can actually be driven by pain. For example, a dog with separation anxiety who is being destructive when left alone, by compulsively digging carpets and doorframes is treated for anxiety by traditional behaviour modification but continues their digging behaviours. Undiagnosed pain in their rear leg was actually causing the dog to redirect by digging through their front legs. These were two entirely separate issues that could easily be misunderstood to be one problem. Resource guarding is another common secondary issue where pain is an underlying factor. Often this can present as a dog guarding a space or item near to where they are laying but the reality is that the pain the dog is experiencing means that moving away from that area or item will cause the pain to be exacerbated so they are merely expressing their discomfort and reluctance to move.

Unwanted behaviour exacerbated by pain

In some scenarios pain does not actually cause unwanted behaviour but simply worsens existing problematic behaviours. Pain and behaviour have a bidirectional relationship; stress due to fear, frustration or anxiety can exacerbate negativity which in turn will increase the dog’s perception of pain. Pain in return can increase stress. Musculo-skeletal pain can be enhanced from anxiety tension. These responses can appear out of proportion and excessively intense. Pain creates a negative cognitive bias within dogs which can lead to exacerbating these issues. This in turn creates a bidirectional relationship as the dogs who are suffering with negative affective states such as anxieties, fears and frustrations are potentially more sensitive to pain.

If the severity of a problem seems disproportionate to the cause of pain, such as the intensity of the dog’s reaction then pain should always be considered. One study (Barcelos et al 2015) notes that dogs experiencing chronic pain would display aggression to a larger range of subjects, both familiar and/or unfamiliar, humans and/or dogs while another study (Fagundes et al) identified several factors suggestive of pain involvement when studying noise sensitive dogs, some suffering with musculoskeletal pain. Those dogs who were suffering with musculoskeletal pain were more likely to generalise their fears (which is believed to occur when these animals tensed due to the noises they were fearful of) which meant their pain was exacerbated which in turn led to a far wider generalisation. Dogs experiencing pain are also less inclined to seek out comfort from their owners and more likely to hide which is believed to be in an attempt to avoid due to the association of hugging or cuddling from humans as our well meaning but sometimes misguided attempt to reassure the dog. Unfortunately such actions could in fact increase the pain the dog is experiencing if we are unaware of the location of pain.

Behaviours that may not be problematic but indicate pain

·      Shaking their head

·      Scratching

·      Laboured breathing

·      Sitting side saddle

These are all behaviours that could easily be normalised as typical dog behaviours and in turn ignored by owners but these could also be indicative of a level of pain and should always be checked out and considered. There are many intricate and much more subtle signals that pain is being experienced. Many are understandably missed as they resemble perfectly normal behaviours, for example self-mutilating behaviours like excessive licking, biting or scratching one particular area of the body could easily be overlooked as simple enthusiastic grooming, a dog seeking more affection than normal could be misconstrued as being a ‘needy’ pet and active avoidance or hiding from people which could be thought of as being shy or fearful. Excessive licking often be associated with dogs suffering discomfort or pain from gastro-intestinal disorders and research has shown that even if no actual GI disorder was identified in dogs who were excessive lickers, nausea and pain from hyperacidity could be a factor as when a dog is then placed onto a hypoallergenic diet with antacid, this behaviour noticeably decreased. Fly snapping and star gazing can also both often indicate underlying gastro-intestinal issues. Both of these involve the upward raising of the dogs head and neck extension which can indicate pain relating to gastric issues. Many dogs experiencing pain, especially in their later years, may start to avoid things they have readily done previously, such as displaying reluctance to jump up onto furniture or into a vehicle, preferring to remain downstairs to avoid having to climb and descend stairs, weight shifting when sitting and reluctance to move their heads in certain ways that were previously easily done. It is important to also acknowledge that some behaviours have become normalised in certain breeds which is making them harder to be recognised as a pain indicator. Jack Russells often have a skip or hop to their movement which can be seen as a normal gait within that breed but this could also be symptomatic of a luxating patella. Sitting side saddle or in a lazy sit is often synonymous with an abnormal gait. Dogs with an abnormal gait are in turn more likely to display irritability, a reluctance to jump up or go for a walk and also more likely to have adjunctive behaviours such as scratching, fly snapping or air licking. Phantom scratching is another behaviour often overlooked. This is where a dog appears to scratch towards one shoulder or their neck region without actually making contact with the skin. This is often associated with syringomyelia which is a neurological condition affecting the spinal cord. Whether these behaviours are indicators of pain or adjunctive is uncertain so for many professionals these behaviours are referred to as adjunctive.  Some dogs will perform displacement behaviours or calming signals such as yawning to increase endorphin release in an attempt to alleviate some physical discomfort.

Pain is a massive factor in why a dog may react with an aggressive response but one of the biggest difficulties in this is that dogs are exceptionally good at masking pain. Dogs have evolved with an inherent instinct to disguise any injuries or vulnerabilities as their origins as predators that hunt dictates that any animal with such weaknesses is vulnerable to attack and reduces their chances of survival. This has continued into today’s modern dogs who still suppress some more obvious indicators of injury or pain which makes it tricky for us humans to realise when our dogs are suffering. It is unknown whether dogs feel pain in exactly the same was as humans do but as mammals all share the same components like the same nervous system, neurochemicals, emotions and perceptions it is likely.

Pain can be a very influential factor in a dog’s behaviour. Pain  induced responses can  be attributed to many behavioural changes as well as physiological changes. Pain is a stressor and extended exposure to pain can cause the whole body to become affected by the stress hormones released in response to the pain. This can cause all the systems and organs to become dysfunctional as well as causing the dog to become exhausted as the stress caused by the pain reduces their appetite, causes fatigue and breakdown of body tissue which also takes away the much needed healing sleep that all bodies need to repair. Dogs experience pain the same way that we do, as an emotional response. The injury or damage occurs and the brain is notified by the nervous system. All brains (human and canine) are individual and will process this information uniquely but all of us will experience pain and our behaviour will be adapted to protect the injury site and prevent us from repeating what we did in future. There is some thought that personality also has a bearing on how a dog will (and again humans too!) experience pain. Some research has shown that dogs with a more extroverted personality or neurotic tendencies are more likely to display more obvious signs of experiencing pain, such as vocalisation and worrying the injury site.  

Dermatological problems can be another contributing factor to a dog displaying aggressive responses. Pruritus, abnormal itching occurs in many cases of skin diseases and often manifests due to secondary infections. Allergies are another irritation for dogs and can cause inflammation and itching. These can be environmental or through consumption of food. There are many dermatological disorders that could affect a dog’s behaviour as well as many other illnesses having an affect on the skin causing dermatological issues which in turn cause more discomfort or pain to the dog. In some dogs excessive licking or grooming of a specific area can indicate another issue. Excessive licking is determined as any licking that the intensity, duration or frequency of attention cannot be justified with normal exploration of the area. Often this licking can cause further a dermatological issues such as soreness or lick granuloma areas but could be associated with many underlying gastro intestinal disorders.

Avoidance of certain contexts having experienced pain previously is not uncommon and a dog may display passive or overtly aggressive behaviours in an attempt to avoid. Dogs are inherently hardwired to seek out pleasure and to avoid pain. Psychologist William James wrote that pleasure is a “tremendous reinforcer” of behaviour and pain is a “tremendous inhibitor” of behaviour which is absolutely true within dog behaviour.

Pain or the fear of pain can cause agonistic responses. Most dogs will show a strong fear response towards pain. Animals learn from painful experiences in the same way humans do. Dogs in pain that display aggressive behaviours are often exhibiting a defensive reaction in an attempt to avoid incurring further injury or pain. When pain is an unconditional stimulus, a fear response is highly probable. When the dog is then in the same situation, they will create associations between the stimulus that caused the pain and neutral stimuli to try and help them predict pain in the future. This fear of pain can then be seen even if the unconditioned stimuli is not present but the associated neutral stimuli is. The anticipation of pain is a great motivator for some dogs. When a dog has previously experienced pain, it is likely that the dog has also experienced a stress response to that pain. There are many behavioural and physiological changes that occur from pain-induced responses. Serotonin activity in the brain decreases and if this is synonymous with physical activity decreasing due to the physical pain then the central nervous system will also see a further reduction on serotonin activity. This reduction in serotonin within the central nervous system has been related to aggressive behaviours.

There are many genetic diseases that can cause a dog to suffer with pain. Some of the diseases cause chronic pain whereas other dogs may suffer intermittent or episodic pain. Dogs affected by genetic disorders should not be used to breed from and genetic testing should be utilised to ensure dominant disease -liability genes are replaced with normal-testing genes to protect any puppies.

Genetics

Allergic skin diseases such as pruritus, recurrent hot spots and chronic inflammatory otitis (ear infections) can affect all breeds of dog but some dog breeds are more predisposed to being affected than others.  One study showed Golden and Labrador retrievers having a 47% heritability for atopic dermatitis although there is no genetic-liability testing available.

Hip dysplasia can cause severe pain for any dog that suffers from this disease. Hip dysplasia is indiscriminate in which dogs it affects but it is the most common inherited disease. Over 40 percent of Golden and Labrador Retrievers are affected. (22)  Smaller dogs although they may suffer with the disease often do not display the same pain that is demonstrated by larger breeds which shows there may be a correlation between size and weight and the impact of the disease. Dysplasia can also affect elbows.

Patellar luxation is complexly inherited and causes pain when the kneecap pops out. This disease is more common in smaller breeds.

There are many more genetic disorders but the above are some of the most common in causing pain and in turn elicit aggressive responses towards humans being near or handling the dog. (23)

CONCLUSION

No two animals will behave identically when experiencing the same illnesses or pain. There are many factors that can affect the expression of behaviours including genetics, life experiences, pre-natal influences and the function of internal organs and body systems. Medical issues are likely to alter a dog’s behaviour both directly or indirectly. The most frequently seen sign of pain is a change in behaviour and usually that behaviour will be have to be seen as problematic enough by the owner to initiate any veterinary investigations. Many medical conditions are only discovered after behavioural changes which lead to further investigation. It is imperative that any veterinarians and behaviour professionals keep in mind the potential influence that pain may have on a dog’s behaviour when working with a dog displaying aggressive responses. All the current research suggests it is better to treat suspected pain prior to any behaviour modification attempts rather than only consider this once the dog fails to respond to any modifications. Pain can be a leading cause of aggressive responses being demonstrated by a dog. We as humans need to be more alert to the fact that dogs hide pain exceptionally well and we need to read the subtext that our dogs are telling us when their behaviour tells us that something is wrong. Dogs rarely choose aggression for no reason and if there is suddenly a change in the dog’s temperament or behaviour then a medical rule out is imperative to ensure that pain as a factor is not overlooked.

I am part of a blog circle of amazing canine professionals, please click here to read Paws & Claws Neston’s article on Pain Awareness

Written by Clare Jarmaine

                                            Dog Behaviour Trainer

                                        Canine InTuition