Systematic pain assessment in horses

•Accurate and reliable pain recognition and quantification are necessary for adequate pain management in horses.•Multiple pain scoring tools (pain scales) have been developed and evaluated for use in equine clinical pain states.•Multidimensional pain scales show higher agreement between different observers than other pain scales (VAS, NRS).•Facial expression pain scales appear easy to use and sensitive, showing great promise for application in clinical practice.

Accurate recognition and quantification of pain in horses is imperative for adequate pain management. The past decade has seen a much needed surge in formal development of systematic pain assessment tools for the objective monitoring of pain in equine patients. This narrative review describes parameters that can be used to detect pain in horses, provides an overview of the various pain scales developed (visual analogue scales, simple descriptive scales, numerical rating scales, time budget analysis, composite pain scales and grimace scales), and highlights their strengths and weaknesses for potential clinical implementation. The available literature on the use of each pain assessment tool in specific equine pain states (laminitis, lameness, acute synovitis, post-castration, acute colic and post-abdominal surgery) is discussed, including any problems with sensitivity, reliability or scale validation as well as translation of results to other clinical pain states. The review considers future development and further refinement of currently available equine pain scoring systems.