Development of the Horse Grimace Scale (HGS) as a pain assessment tool in horses undergoing routine castration.
Authors: Dalla Costa Emanuela, Minero Michela, Lebelt Dirk, Stucke Diana, Canali Elisabetta, Leach Matthew C
Journal: PloS one
Summary
# Editorial Summary: Development of the Horse Grimace Scale Facial expression has long been recognised as a valuable pain indicator in humans and other species, yet equine pain assessment has traditionally relied on behavioural observations that can be inconsistent and context-dependent. Dalla Costa and colleagues set out to develop and validate a standardised facial grimace scale specifically for horses, using animals undergoing routine castration as their study population—a procedure commonly performed in practice where reliable, non-invasive pain assessment would be clinically valuable. The researchers identified and quantified specific facial features (ear position, eye tightness, muzzle tension, and nostril/mouth shape) that changed measurably in response to pain, ultimately creating a five-point ordinal scale applicable to video recordings or direct observation. Key findings demonstrated that the Horse Grimace Scale reliably differentiated pain states, with facial expressions showing significant changes during acute pain phases that correlated with other established pain indicators, making it a practical tool for everyday use by farriers, veterinarians, and handlers without requiring specialised equipment. For practitioners, the HGS offers a straightforward, objective method to assess post-operative discomfort and treatment response in castrated horses and potentially other painful conditions, filling an important gap in equine welfare assessment and helping inform decisions about analgesia provision and recovery management.
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Practical Takeaways
- •Use HGS as a quick, non-invasive pain scoring method during and after routine procedures like castration—no special equipment needed, just visual observation
- •Standardized facial expression assessment can improve pain management protocols by enabling faster, more consistent pain recognition across different handlers and settings
- •Implement HGS in your pain monitoring toolkit to better evaluate welfare outcomes and refine anesthesia and analgesia protocols for standing and recovery procedures
Key Findings
- •Horse Grimace Scale (HGS) was successfully developed as a standardized facial expression-based pain assessment tool for equines
- •HGS provides a non-invasive alternative to existing pain assessment methods with improved applicability in routine clinical and management procedures
- •Facial expression changes are reliable indicators of pain severity in horses undergoing castration