On-going studies : coding facial expression of pain in horses (Horse Grimace Scale)

The assessment of pain in animals is particularly difficult because there is no verbal means of communication between animals and humans. The human facial expressions of pain have been coded using a facial action coding system and they are reliably used to assess pain in neonates. The approach used in human infants can provide a framework for animal pain assessment. Langford and colleagues (2010) applied for the first time the facial action coding system for studying pain expression in animals: they developed the Mouse Grimace Scale (MGS), a standardized facial coding system of mice pain facial expressions. The aim of this study is to develop and validate a standardized scale of facial expressions of pain in horses (Horse Grimace Scale). Ten stallions of different breed and age were placed in an observation box with two digital high resolution video cameras positioned at opposite corners of the box. All the subjects werecastrated with closed technique in general anaesthesia and their behaviour was video recorded at scheduled time (before and 8 hours after surgery). Compared to basal, 8 hours after castration horses showed significantly more pain related behaviour. To develop the grimace scale we grabbed video frames (pictures) from videos every time the face of the horse is clearly visible before and after surgery. Then we cropped the resultant JPEG files such that body position is no longer visible. We compiled collages of “no pain” (basal condition) and “pain” (8 hours after surgery) photographs for each subject with the head oriented in the same position. We will then collaborate with experts in coding facial expression of pain in other species to identify horse facial features of pain and define different action units. Possible action units, as already described in other animals such as mice, sheep, and horses will be orbital tightening, eye squeezed, ear position. Using collages of pictures we will ask to people with different experience with horses to identify facial expression of pain.