Changes in the equine facial repertoire during different orthopedic pain intensities

Abstract

A number of facial expressions are associated with pain in horses, however, the entire display of facial activities during orthopedic pain have yet to be described. The aim of the present study was to exhaustively map changes in facial activities in eight resting horses during a progression from sound to mild and moderate degree of orthopedic pain, induced by lipopolysaccharides (LPS) administered in the tarsocrural joint. Lameness progression and regression was measured by objective gait analysis during movement, and facial activities were described by EquiFACS in video sequences (n = 348, total length 892.5 minutes) of the horses obtained when resting in their box stalls. Predictive modeling identified 16 action units and action descriptors, related to ears, eyes, and lower face. Lower lip depressor (AU16), lips part (AU25), half blink (AU47), single ear forward (SEAD101) and single ear rotator (SEAD104) were selected as co-occurring significantly more in horses with pain than in horses without pain. The major change in co-occurring facial activities occurred in the transition from no pain to mild pain. In conclusion, resting horses with induced orthopedic pain showed a dynamic upper and lower facial repertoire and the relationship between level of pain intensity and facial activity appears complex.

Science‐in‐brief: Highlights from the abstracts at the Ninth International Conference on Canine and Equine Locomotion, Utrecht, 2023

“…However, further research is required to identify facial displays of pain in naturally lame horses. 12 At present, the influence of facial pressure exerted by noseband type and/or tightness on facial structures is unknown. However, research presented at ICEL9 on this topic showed that the noseband type and/or tightness can significantly affect facial pressure both standing, 13 and when ridden at trot, 14 and can even have an effect on eye temperature, an indicator of stress.…”