Identification of Body Behaviors and Facial Expressions Associated with Induced Orthopedic Pain in Four Equine Pain Scales

Abstract

Equine orthopedic pain scales are targeted towards horses with moderate to severe orthopedic pain. Improved assessment of pain behavior and pain-related facial expressions at rest may refine orthopedic pain detection for mild lameness grades. Therefore, this study explored pain-related behaviors and facial expressions and sought to identify frequently occurring combinations. Orthopedic pain was induced by intra-articular LPS in eight horses, and objective movement asymmetry analyses were performed before and after induction together with pain assessments at rest. Three observers independently assessed horses in their box stalls, using four equine pain scales simultaneously. Increase in movement asymmetry after induction was used as a proxy for pain. Behaviors and facial expressions commonly co-occurred and were strongly associated with movement asymmetry. Posture-related scale items were the strongest predictors of movement asymmetry. Display of facial expressions at rest varied between horses but, when present, were strongly associated with movement asymmetry. Reliability of facial expression items was lower than reliability of behavioral items. These findings suggest that five body behaviors (posture, head position, location in the box stall, focus, and interactive behavior) should be included in a scale for live assessment of mild orthopedic pain. We also recommend inclusion of facial expressions in pain assessment.

Towards Machine Recognition of Facial Expressions of Pain in Horses

“…Some of the most widely used horse pain scales involve social interaction between the observer and the horse, that is, touching, feeding the horse or palpating the sore area [18]. A recent study [79] showed that these types of scales generally perform well, but if the pain is evaluated using one of these scales by direct observation, video recordings for CV/ML purposes should be made immediately before the direct pain scoring. It is also important to test the system in another population of horses, to prevent reliance on spurious correlations.…”

“…To determine whether a pain scale can deliver ground truth, it is necessary to know the performance parameters of the pain scale used for the actual population tested during the actual conditions. Surprisingly, few pain scales are adequately validated in this regard [54,79] since sensitivity and specificity can only be measured against ground truth. In horses, a number of pain assessment scales based on facial expressions have been presented recently.…”

“…Many management and treatment procedures are indeed quite painful in humans as in horses, and filming of clinical procedures may yield information about facial expressions, which, however, may be blended with other affects. Fully reversible short-term pain induction treatments in horses include a sole pressure model [96], an inflammatory joint model [79,97,98], a non-invasive ischemic pain model [81] and a capsaicin skin sensitization model [81]. An experimental setup allows recording of proper baseline behaviors, while the short-term pain model predicts the time points for pain and subsequent relief of pain.…”

Equine Discomfort Ethogram

“…A search of veterinary, animal science, and equine behavior science literature (English language, from mid 20th century to the present) was undertaken to identify research reports and review articles or book chapters describing behaviors associated with physical discomfort in horses. Forty-five such sources [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ] were reviewed to confirm agreement with our identified behaviors, as well as to identify any behavioral elements or sequences reported to reflect physical discomfort in horses that had not been identified in our clinical observations.…”

Equine Cervical Pain and Dysfunction: Pathology, Diagnosis and Treatment

“…Observing the natural behavior of horses in their home environment is helpful as the stress and excitement of being in unfamiliar surroundings will cause some horses to override signs of pain and discomfort. Behavioral assessment is an important part of the overall examination to take note of [22]. Careful attention should be paid to the horse's stance, facial expressions, and how the horse interacts with its surroundings and humans.…”