Pain in dogs is not always easy to recognize. Unlike humans, dogs lack the ability to communicate emotions with words, but this does not mean that they lack emotions. Overt and obvious signs of pain in dogs, such as vocalization and aggressive reactions in response to palpation or manipulation of a painful area, usually require the occurrence of an extreme painful experience in most dogs. This is perhaps the most easily detectable painful condition by dog owners, but is also only one of the several painful conditions that can occur in dogs. Actually most painful conditions in dogs are characterized by subtle sings and often require a careful observation of dogs' behaviours, as well as their correct interpretation, before being detected. So it is important that pet owners learn how to recognize pain in dogs, in order to avoid unnecessary suffering to their companions.
The evaluation of pain in dogs mainly relies on the observation of their behaviour, with an emphasis on attitude, activity level, posture and locomotion, appetite, grooming, vocalization, facial expression, as well as self-guarding and self-awareness behaviours. Broadly speaking, dogs show three different types of behavioural changes in response to pain, depending on whether pain is acute, sub-acute (or persistent) or chronic.
In acute painful conditions (that is, those immediately following a painful incident) dogs usually show avoidance or escape reactions, whose strength increases as the severity of the painful stimulus does. In the most severe cases vocalization and sudden unusual aggression are not infrequent, especially when dogs are caught by surprise by the painful stimulus or incident. Vocalization may occur as howl, bark, growl, yelp, whine or any combination, while aggressive reaction to palpation of the affected body part may occur as a snarl or even as an attempt to bite or attack human or other animals.
As the pain becomes more persistent (sub-acute pain, such as that following an accidental trauma after the acute phase is over, as well as that following a surgical intervention) dogs usually start to show a more protective behaviour in order to minimize any stimulation of the painful area. In this condition, many signs can be indicators of pain. There may be signs of vocalization, such as whimpers and groans, which often stop when the dog is comforted. Protective and guarding behaviours may include frequent changes in body position in order to find the position that causes the least discomfort, as well as reluctance to use the painful body part with resulting abnormal posture or unusual gait. For example, dogs with a painful limb may limp in order to minimize the weight-bearing on the affected part, while dogs with abdominal or thoracic pain may be reluctant to lie down and may stand for hours until exhaustion. Changes in activity level may also appear as restlessness, agitation and disturbed sleep patterns or, at the other end of the spectrum, as lethargy, dullness and unwilling to move and play. Self-awareness behaviours such as protecting, licking, chewing and looking at the painful body area are always reliable indicators of pain. Changes in facial expression can be used to recognise pain in some dogs, as well. The dog may hold its ears in a down or back position and may have wide open eyes with dilated pupils and sometimes a fixed, glazed stare. On the other hand, its eyes may be also partially closed and have a tired, dull appearance. Furrowing of brows and other unusual grimaces may be facial signs of pain in dogs, as well.
The matter of how to recognise pain in dogs becomes more challenging when talking about chronic pain. The last is defined as a pain lasting for more than 3 months, which can persist beyond or in the absence of the original noxious stimulus and most often is not associated with an obvious external injury, but rather arises from less apparent chronic conditions, such as cancer and osteoarthritis. In this case behavioural signs of pain are usually subtle and non-specific, insidious in their onset and often go unnoticed by the owner or mistaken for signs of normal aging. Depression, irritability, reduced appetite, reduced activity level, failure to groom regularly, disturbed sleep, unresponsiveness to environmental stimuli and poor interaction with the owner may be all signs of chronic pain in dogs, which in the most advanced stages culminate in lethargy, withdrawal from the surroundings and from social interactions, weight loss, muscle wasting and a complete loss of body condition. Other typical signs of chronic pain include a lowered pain threshold and resulting increased responses to painful stimuli, as well as the occurrence of painful reactions to stimuli that do not normally cause pain. Because of the very debilitating nature of chronic pain, it is important that pet owners learn how to recognise pain in dogs in order to avoid the devastating consequences of this condition on the quality of life of their pets. And it is also important that owners keep track of any suspicious behavioural changes in their dogs, because these are often only apparent in the home setting and can be masked by misleading behaviours during routine veterinary visits. This might be a demanding task for pet owners, but is the best way to allow the veterinarian to make a diagnosis of chronic pain as early as possible and formulate an appropriate management plan aimed at maximising the quality of life of dogs with chronic pain.