Assessing fear of novel and startling stimuli in domestic dogs

Dog attacks on humans are a community issue and, while defensive and offensive aggression are implicated, little is known about the motivational basis of these attacks. Defensive aggression arising from fear may be implicated in some attacks and thus research on measuring fear in dogs is clearly required. The aim of the present study was to examine the validity of several measures of fear of novel and startling stimuli previously identified in the authors' laboratory. Anxiolytic drugs have been shown to reduce fear behaviour in rats in novel situations and thus an anxiolytic drug, clomipramine, was used in the present study to examine the validity of these previously identified measures of fear. Twenty-four dogs of varying breed, age and sex were used in a cross-over design, involving a placebo treatment and a clomipramine treatment. It was found that when the dogs were medicated with clomipramine for 6 weeks they were quicker to approach and spent more time near the stimulus (P < 0.05) in a novel object test. Furthermore, there was a tendency (P = 0.06) for a treatment by order interaction in which treatment with clomipramine in the first period but not the second period was associated with reduced latency to approach and increased time spent near the stimulus in the startling test. There was no treatment effect on latencies and entries to areas in a light/dark test and an elevated plus maze test. These results indicate that a number of behavioural variables in two of the tests, the novel object and startling test, are measures of fear of novel and startling stimuli, respectively, in dogs and furthermore provide a useful methodology to study fear-induced aggression in dogs.