09/16/2026
Six facial regions. A three-point score for each. That is the Horse Grimace Scale, developed by Dalla Costa and colleagues at the University of Milan and published in 2014 as part of the EU-funded AWIN project.
It was built on forty stallions filmed before and after routine castration, with facial changes coded frame by frame against known pain states. The six scored items are ear position, orbital tightening, tension above the eye, strained chewing muscles, a strained mouth with pronounced chin, and strained, flattened nostrils.
The scale has since been validated for naturally occurring pain too, not just surgical pain, with a 2016 study confirming it holds up in horses with acute laminitis. It is not infallible everywhere. Evidence for some conditions, such as gastric ulcer syndrome, has been weaker, and researchers continue refining the tool, including a 2024 update to its anatomical descriptors.
Used properly, alongside behaviour and veterinary judgement, it gives a structured way to notice pain that might otherwise go unseen.