Changes in facial expressions during short term emotional stress as described by a Facial Action Coding System in horses

Sammanfattning: Animals subjected to stress is a well-known issue that has to be taken into account when working in a clinical environment. A stress response is closely related to several physiological and behavioural effects that could potentially mask symptoms of pain. So far, research has focused on evaluating stress using ethograms or physiological indicators. However, little has been focused on using facial expressions when evaluating stress. This is important because only a little research regarding facial expressions of pain has considered the potential of other emotions affecting the readings. Therefore, this thesis discusses the concepts of pain and stress and how they work together, as well as methods for objectively evaluate pain and stress, using literature available today. An observational semi-randomized pilot study containing six horses was performed with the objective to generate hypotheses and methodology for further studies in the area. The horses were video filmed in their own stable without observers approximately sixty minutes to collect a baseline. These films were annotated in ELAN software using the Equine Facial Action Coding System. These horses were then subjected to an emotional stressor, transportation by road, and filmed in the transport for approximately twenty minutes. During baseline filming and filming during transportation, heart rate was collected using an equine electrode transmitter that was applied on the horses’ heart silhouette. This was done to get an indication of the susceptibility to stress of the horses measured. All horses showed an increase in heart rate during transportation. The changes in the horses’ facial expressions were shown through descriptive statistics with some significance testing. The transported horses overall showed tendencies to tension in certain facial muscles, since the frequency of nostril dilation (p=0.005) and upper eyelid raiser (p=0.02) increased during transportation. The transported horses also experienced a more extrovert behaviour regarding blinking, ear- and head movements. The frequencies of these movements increased during transportation. This thesis concludes that horses do express an increased frequency of certain facial expressions during emotional stress. It is anticipated that these may potentially affect pain evaluation using the equine pain face. However, further studies with a larger population is needed to draw further conclusions.