The impact of multiple exposures and movement on the fear response of poultry

Fear tests are a common research method to assess the affective state of an animal. This study aimed to assess: 1) the impact of repeated exposure to fear tests on fear response and, 2) how the addition of movement to fear stimuli during a novel object test impacts bird fear response. Over two trials, a total of 3,600 Ross 308 birds (1800 birds/trial) were raised until 42 days of age. At 23d, 30d, and 37d, three fear tests were performed, novel object, human approach, and response to observer tests. The novel object test was split into three movement treatments, stationary, intermittent, and continuous. The response to observer test was performed before and after the other tests. Data from the human approach test was analyzed for age effect by ANOVA. Novel object data was analyzed as repeated measures ANOVA for the effect of movement. Differences in response to observer were analyzed using a paired T-test. Repeated exposure to fear test within the same day decreased the fear response, with response to observer results before fear testing (66%) differing from after (42%, P<0.01). The fear response also decreased with multiple consecutive exposures. Both latency to human approach and latency to novel object interaction were longest on 23d, then 30d, and shortest on 37d (P<0.01). For both the human approach and the novel object test, at all-time points, the number of birds interested in the human or object was higher on 37d than 23d (P<0.01). The addition of movement to the novel object test increased the fear response at 23 days but decreased the fear response at 37 days. Overall, the repeated exposure of birds to fear tests reduced the bird's fear response, both for the repeated exposure to different fear tests on a single day and the repeated exposure to one type of fear test over the length of a flock. This impact of repeated exposure is important to recognize when designing experiments that utilize fear tests.