Partners with bad temper: Reject or cure? a study of chronic pain and aggression in horses

Abstract

Background: Experiencing acute pain can affect the social behaviour of both humans and animals and can increase the riskthat they exhibit aggressive or violent behaviour. However, studies have focused mainly on the impact of acute rather thanchronic painful experiences. As recent results suggest that chronic pain or chronic discomfort could increase aggressivenessin humans and other mammals, we tested here the hypothesis that, in horses, aggression towards humans (a commonsource of accidents for professionals) could be linked to regularly reported vertebral problems of riding horses.Methodology/Principal Findings: Vertebral examination and standardized behavioural tests were made independently onthe same horses. Here we showed that most horses severely affected by vertebral problems were prone to reactaggressively towards humans (33/43 horses, chi-square test, df = 1, x2 = 12.30, p<0.001), which was not the case forunaffected or slightly affected horses (9/16 horses, chi-square test, df = 1, x2 = 0.25, p>0.05). The more affected they were,the fewer positive reactions they exhibited (rs =20.31, p = 0.02).Conclusions/Significance: This is to our knowledge the first experimental evidence of such a link between chronicdiscomfort/potential pain (inferred from the presence of vertebral problems) and aggression, suggesting that chronicpainful experiences may act in ways similar to those of acute experiences. Chronic discomfort or pain may often beoverlooked when facing "bad tempered" individuals, whether humans or animals. This experimental study confirms theimportance of including chronic discomfort or pain as a major factor in interpersonal relations and models of aggression.© 2010 Fureix et al.