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horses.
The Horse Grimace Score (HGS) is a facial expression-based pain assessment tool that evaluates specific facial changes, including: ears held stiffly backward, orbital tightening, glazed or withdrawn expression, tightening of the mouth and lips, strained nostrils, increased facial muscle tension.
While it has been successfully used for evaluating pain associated with lameness and colic, its effectiveness in detecting dental pain remains uncertain.
Dental disease is a common issue in horses, with conditions such as equine odontoclastic tooth resorption and hypercementosis (EOTRH) and equine periodontal disease (PD) being recognised as painful.
Given the importance of accurately assessing pain, a small study was conducted to evaluate and compare the usefulness of the Horse Grimace Score and a numerical rating scale (NRS) for assessing dental pain in horses with dental conditions.
The study, by Amelia Sidwell and colleagues at the University of Nottingham veterinary school in conjunction with the Pool House Equine Hospital aimed to see if a pain scale based on facial expressions (HGS) provided an objective assessment of pain in equine dental cases.
An additional aim was to identify whether specific dental conditions are associated with greater pain severity. A full report of the research is published in the Veterinary Record.
Twelve horses that had been admitted to a referral equine referral hospital for tooth extraction were included in the study. Diagnoses included: cheek tooth fracture (5 cases), periapical tooth infection (3), developmental disorders (2), periodontal disease (PD) (1), EOTRH (1).
Each case was assessed for pain by an experienced clinician using both a HGS and a numerical rating score. In addition, photographs of the head showing facial expressions were incorporated into a questionnaire which was submitted to equine veterinary surgeons, nurses, and final-year veterinary students for evaluation.
The research team found that there was poor correlation between individual observers using both pain scales, suggesting low reliability in assessing dental pain. The highest mean pain scores were associated with periodontal disease and EOTRH, aligning with existing literature on the painful nature of these conditions.
They concluded that tools designed for identifying acute pain (such as HGS) are unreliable for assessing chronic pain like dental pain. They recommended the development of a dental-specific ethogram to more accurately assess dental pain in horses.
For more details, see:
Sidwell AE, Duz M, Hill B, Freeman S, Hole SL.
Application of the horse grimace scale in horses with dental disease: Preliminary findings.
Veterinary Record. (2025) 196(3):e4800.
https://doi.org/10.1002/vetr.4800
