Dental problems can cause significant discomfort and pain in horses. Sadly, many horses do not demonstrate obvious clinical signs of dental pain leading to delayed diagnosis and treatment which could impact welfare and performance for affected horses.
A technique to identify equine pain behaviors using equine facial expressions, the Horse Grimace Scale (HGS), was employed to examine the effect of dental disorders on wellbeing in horses1. Facial expression as a way to monitor pain has been developed for a wide range of species and is proving to be a reliable and sensitive way to identify and record the experience of pain without obvious clinical signs being expressed.
The HGS evaluates six equine facial expression characteristics relating to; the nostrils, mouth and chin, jaw/chewing muscles, the area around/above the eye and ear position. In general, a “painful face” has been described as; low/asymmetrical ear position, angulated eyes, a withdrawn/tense stare, nostrils dilated towards the center of the face and tension of the chin, lips and other facial muscles2. Pain after castration has been examined using the HGS3 and it has also been used to identify and assess pain in horses with acute colic4.
The study aimed to examine any changes in facial expression in horses with dental disorders before and after treatment/management, explored the consistency of observers scoring from photographs or physical presence, and compared the outcomes from trained HGS observers to those scoring subjectively. Thirty-three horses (2.5-14 years old, 13 males and 20 females) in work were included. None had any dental treatment for a minimum of six months prior to the study. All horses were assessed in-person using the HGS before dental examination/diagnosis and again 15 days after treatment. Photographs were also taken at both time points for subsequent blind analysis by three veterinary surgeons trained in HGS and four veterinary surgeons who scored the photographs for pain based on their clinical experience.
Results revealed that all study horses had at least one dental disorder, with many presenting with multiple conditions , including excessive enamel points, hooks, ramps, mouth ulcers, periodontitis or retained deciduous teeth. The use of the HGS before and after treatment suggested that changes in HGS scores could be identified in the study horses, both from the physically present assessor and those scoring from photographs. There were also reductions in HGS scores (p <0.05) after appropriate treatment, despite the horses not having displayed obvious clinical signs of pain previously. Two of the four assessors scoring by subjective evaluation identified reduced pain scores following treatment. The use of HGS thus had a high degree of reliability and score consistency across trained observers, in contrast to the subjective assessment of photographs by non-HGS trained veterinary surgeons, which was less consistent and effective in identifying pain or a reduction in pain.
This study demonstrated that the HGS is reliable, effective and consistent for the assessment of pain associated with dental disorders in horses.
1. Coneglian, M.M., Borges, T.D., Weber, S.H., Bertagnon, H.G. and Michelotto, P.V. (2020). Use of the horse grimace scale to identify and quantify pain due to dental disorders in horses. Applied Animal Behaviour Science, 225, 104970. Available HERE
2. Gleerup, K.B., Forkman, B., Lindegaard, C. and Anderson, P.H. (2015). An equine pain face. Vet. Anaesth. Analg., 42, 103-114.Available HERE
3. Dalla Costa, E., Minero, M., Lebelt, D., Stucke, D., Canali, E., and Leach, M.C. (2014). Development of the Horse Grimace Scale (HGS) as a pain assessment tool in horses undergoing routine castration. PLoS One, 9, 1-10.Available HERE
4. VanDierendonck, M.C. and van Loon, J.P.A.M. (2016). Monitoring acute equine visceral pain with the Equine Utrecht University Scale for Composite Pain Assessment (EQUUS-COMPASS) and the Equine Utrecht University Scale for Facial Assessment of Pain (EQUUS-FAP): a validation study. Vet. J., 216, 175-177. Available HERE