Pain-related aggression in dogs: 12 clinical cases

Abstract

The aim of this retrospective study was to describe the main features of pain-related aggression in dogs. Twelve dogs presented for aggressive problems at the Veterinary Hospital of the Autonomous University of Barcelona, Spain, were included, and a questionnaire was used to gather information on the context of the aggression, body posture during the attack, impulsiveness, and aggressive behavior before the onset of the pain-eliciting condition. The most common cause of pain was hip dysplasia (66.7%), but no relationship was found between the cause of pain and the characteristics of the aggressive behavior. Dogs were classified as having been aggressive before or after the onset of painful condition. Dogs that had not been aggressive before the onset of the pain-eliciting condition were more impulsive (df = 1, χ² = 5.3, P = 0.0209), showed aggression as a result of manipulation context more frequently (df = 1, χ² = 6, P = 0.0143), and adopted a defensive body posture more frequently (df = 1, χ² = 3.733, P = 0.0533) than dogs that had been aggressive before the onset of pain. These results suggest that previous expression of aggressive behavior has a major effect on the pattern of pain-related aggression in dogs.

Introduction

The International Association for the Study of Pain (IASP, 2011) defines pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.

The most common sign of pain in animals is a change in behavior (Hellyer et al., 2007). Behavioral signs of pain include both the loss of normal behaviors and the development of new and abnormal behaviors. The most common behaviors classified as “lost normal behaviors” are decreased ambulation or activity, lethargic attitude, and decreased appetite, and the most common “developed abnormal behaviors” are aggression, fear reactions, inappropriate elimination, vocalization, decreased interaction with other pets or family members, altered facial expression, altered posture, restlessness, and hiding (Hellyer et al., 2007).

It is widely accepted that pain can cause aggressive behavior that is often described as a defensive reaction to avoid physical contact that may cause further injury (Rutherford, 2002).

Pain elicits a stress response (Mellor et al., 2000). Pain-induced stress responses lead to increased production of cortisol, catecholamines, and inflammatory mediators that cause tachycardia, vasoconstriction, decreased gastrointestinal motility, delayed healing, and sleep deprivation. Pain, especially chronic pain, also causes unseen changes in the central nervous system (CNS) that can lead to magnification of pain perception, through allodynia and hyperalgesia, and a prolonged pain state (Hellyer et al., 2007).

Pain-induced stress response may reduce serotonin activity in the brain (Mellor et al., 2000). Pain could also decrease physical activity and this may further reduce serotonin activity in the CNS (Chaouloff, 1997). A reduction of serotonin activity in the CNS has been related to aggressive behavior in dogs (Tsatsoulis and Fountoulakis, 2006). Whether changes in serotonin activity caused by pain may result in a pattern of aggressive behavior different from that caused by a defensive reaction is unknown.

The aim of this study was to describe the main features of pain-related aggression in dogs, including its context, the dog’s body posture, and whether the dog reacted impulsively.