Can the presence of musculoskeletal pain be determined from the facial expressions of ridden horses (FEReq)?

Poor performance in horses is often attributed to rider or training problems or behavioral abnormalities. Riders often fail to recognize lameness. We need to determine if there are differences in facial expression in lame and nonlame horses when ridden, which may facilitate the identification of horses experiencing pain. A previously developed facial expression specific for ridden horses ethogram was applied blindly by a trained analyst to photographs (n = 519) of the head and neck of lame (n = 76) and nonlame (n = 25) horses acquired during ridden schooling-type work at both trot and canter. These included images of 7 lame horses acquired before (n = 30 photographs) and after diagnostic analgesia had abolished lameness (n = 22 photographs). A pain score (0-3; 0 = normal, 1-3 = abnormal) was applied to each feature in the ethogram, based on published descriptions of pain in horses. Pain scores were higher for lame horses than nonlame horses (P < 0.001). Total pain score (P < 0.05), total head position score (P < 0.01), and total ear score (P < 0.01) were reduced in lame horses after abolition of lameness. Severely above the bit, twisting the head, asymmetrical position of the bit, ear position (both ears backward, one ear backward and one to the side, as well as one ear backward and one ear forward), and eye features (exposure of the sclera, the eye partially or completely closed, muscle tension caudal to the eye, and an intense stare) were the best indicators of pain. Application of the facial expression specific for ridden horses ethogram and pain score could differentiate between lame and nonlame horses. Assessment of facial expression could potentially improve recognition of pain-related gait abnormalities in ridden horses.