Are Eyes a Mirror of the Soul? What Eye Wrinkles Reveal about a Horse's Emotional State.
Authors: Hintze Sara, Smith Samantha, Patt Antonia, Bachmann Iris, Würbel Hanno
Journal: PloS one
Summary
# Editorial Summary: Eye Wrinkles as Emotional Indicators in Horses Researchers at the University of Bern investigated whether changes in eye wrinkle expression around the inner eyebrow could serve as a reliable indicator of emotional state in horses, addressing a critical gap in welfare assessment where objective, non-invasive measures remain limited. Sixteen horses were exposed to positive conditions (grooming and food anticipation) and negative conditions (food competition and visual threat via a plastic bag), with standardised photography and blind scoring of six eye-based measures including wrinkle markedness, number, angle, and eyelid configuration. The most significant finding was that the angle between the eyeball and the highest wrinkle decreased during grooming (positive emotion) and increased during food competition (negative emotion) compared to baseline, though other measures including wrinkle count and eyelid shape showed no consistent response. Whilst this single validated parameter offers promise as a non-invasive welfare indicator—particularly relevant for farriers and handlers assessing horses during routine work—the authors appropriately caution that further research across diverse conditions and contexts is essential before eye wrinkle angle can be confidently applied in clinical or management settings. The work provides a methodological foundation for developing objective, practical tools to evaluate emotional valence in horses, though practitioners should currently regard this as an emerging rather than established assessment technique.
Read the full abstract on PubMed
Practical Takeaways
- •Eye wrinkle angle (specifically the angle between the eyeball line and highest wrinkle) may help identify negative emotional states in horses during management procedures
- •Grooming reduces eye wrinkle markers while competitive or stressful situations increase them—potentially useful for evaluating horse comfort during handling
- •Further research is needed before relying on eye wrinkles as a standalone welfare assessment tool; use alongside other behavioral indicators
Key Findings
- •Eye wrinkle angle decreased during grooming and increased during food competition compared to control phases
- •Inner eyebrow raiser muscle contraction produces measurable eye wrinkle variation in horses
- •Only 1 of 6 outcome measures (wrinkle angle) showed significant variation with emotional conditions
- •Eye wrinkle expression shows potential as a welfare indicator but requires further validation across different conditions