Glossary
Equine grimace scale.
Direct answer
The equine grimace scale is a scoring grid that assesses pain-related signs in the horse through facial expression. Six defined features are scored, among them ear position, partial closure of the eye and tension in the chewing muscles, the mouth and the nostrils. Each feature runs from absent to obviously present.
The grid was developed for acute pain situations and that is where the evidence is strongest. In slowly developing chronic states its reach is smaller, because facial expression responds less distinctly. A single snapshot does not replace repeated observation: scores shift with the situation of the moment.
Confounders are numerous: sedation, head position, exertion, environmental stimuli, and also coat and head shape across breeds. The training of the person scoring matters as well. Methodologically the approach comes from human medicine, where facial coding grids were built for newborns and for people without verbal expression, then reached the horse through rodent work.
The evidence letter
Once a month: new syntheses, checked studies, and what has changed in the state of the evidence.