The look of lameness - Behaviors and facial expressions associated with orthopedic pain in horses

Sammanfattning: There are increasing concerns about equine welfare in equestrian sports, where early detection of orthopedic pain remains a major challenge since reliable and valid pain assessment tools are lacking. Movement asymmetry may be present in horses perceived as free from lameness by their owners, as well as in horses with confirmed orthopedic pain. It is therefore important to differentiate movement asymmetry due to pain from that due to other reasons, which may be achievable by improving orthopedic pain assessment. The aim of this thesis was thus to identify body behaviors and changes in facial activity related to orthopedic pain and movement asymmetry in horses. Progression and regression of movement asymmetry after induced orthopedic pain was monitored and measured with gait analysis in eight horses. A number of behaviors including altered posture, head position, location in the box stall, focus and human interaction were found to be associated with orthopedic pain, as were facial expressions. Only one of four equine pain scales tested detected orthopedic pain reliably and accurately. Dynamic and diverse facial displays were identified in resting and moving horses during pain, illustrating that the concept of one prototypical pain face may be a simplification of the full pain-related facial repertoire. Horses trotted by hand showed a great inter-individual variation in facial expressiveness, highlighting the need for further analysis of facial activity during motion before its use for pain detection. The new knowledge on the relationship between pain and movement asymmetry provided in this thesis, can lead to improved pain assessments, pain management and equine welfare.