Measurement properties of grimace scales for pain assessment in nonhuman mammals: a systematic review

Authors: Evangelista Marina C., Monteiro Beatriz P., Steagall Paulo V.

Journal: Pain

DOI: 10.1097/j.pain.0000000000002474Log in to save

Summary

# Grimace Scales for Equine Pain Assessment: What the Evidence Shows Facial expressions represent a promising non-invasive method for pain evaluation across multiple species, yet the reliability and validity of these assessment tools vary considerably. Evangelista and colleagues conducted a systematic review of 12 grimace scales developed for nine different species, evaluating their measurement properties against established psychometric standards and identifying which instruments have sufficient evidence to support clinical use. The Horse Grimace Scale demonstrated high-quality evidence across multiple measurement properties, whilst the equine-specific EQUUS-FAP and EQUUS-Donkey-FAP scales showed only low levels of evidence, indicating that further validation work is needed before these newer tools can be confidently recommended for routine practice. Notably, whilst construct validity has received considerable research attention, the reliability of these scales—their consistency when used by different assessors or at different times—remains understudied across most species. For equine professionals seeking objective pain indicators beyond traditional behavioural observation, the Horse Grimace Scale offers the most rigorously tested option, though practitioners should remain aware that development and validation of facial expression scales in horses and donkeys continues to evolve and that no single pain assessment tool provides a complete clinical picture.

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Practical Takeaways

•Horse Grimace Scale is among the most validated tools available for equine pain assessment; use it with confidence in clinical and research settings
•EQUUS-FAP and EQUUS-Donkey-FAP require further psychometric validation before relying on them as primary pain assessment tools in clinical practice
•Grimace scales should be used alongside other pain assessment methods (behavioral, physiological) rather than as standalone instruments until measurement properties are more robustly established

Key Findings

•12 grimace scales were identified across 9 species; Mouse, Rat, Horse and Feline Grimace Scales demonstrated high level of evidence for measurement properties
•Rabbit, Lamb, Piglet and Ferret Grimace Scales and Sheep Pain Facial Expression Scale showed moderate evidence levels
•Sheep Grimace Scale, EQUUS-FAP, and EQUUS-Donkey-FAP demonstrated low level of evidence for their measurement properties
•Construct validity was the most frequently reported measurement property while reliability and other validity forms remain understudied

Conditions Studied

pain assessment in nonhuman mammalsfacial expressions of pain

Related References

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