Sex and Age Don't Matter, but Breed Type Does-Factors Influencing Eye Wrinkle Expression in Horses.
Authors: Schanz Lisa, Krueger Konstanze, Hintze Sara
Journal: Frontiers in veterinary science
Summary
# Editorial Summary Facial wrinkles above the eye have emerged as a potential welfare indicator in horses, responsive to both pain and emotional states, yet researchers have not previously examined whether baseline eye wrinkle expression varies with individual characteristics that might confound interpretation. Schanz and colleagues photographed 181 horses in neutral conditions and assessed eye wrinkles using five measures—perceived worry, brow elevation, wrinkle number, wrinkle prominence, and the angle between the eye corners and uppermost wrinkle—with high intra- and inter-observer reliability across all metrics. Breed type was the only factor to significantly influence eye wrinkle expression, specifically the angle measurement, with thoroughbreds showing the narrowest angles (23.80°), warmbloods intermediate (28.00°), and coldbloods the widest (31.00°); age, sex, body condition, and coat colour had no systematic effect. These findings suggest that when using eye wrinkles as an emotional or pain indicator in clinical or welfare assessments, breed type should be considered as a baseline variable, whilst practitioners can disregard age and sex differences—however, further research is needed to establish how reliably eye wrinkles reflect emotional or mental states across different situations, as this study was limited to neutral contexts.
Read the full abstract on PubMed
Practical Takeaways
- •When using eye wrinkles as a welfare or pain indicator, breed type must be accounted for as a confounding variable—thoroughbreds naturally display narrower angles than coldbloods in neutral states
- •Observer agreement on eye wrinkle assessment is reliable, making it a feasible tool for consistent on-farm welfare evaluation
- •Age and sex do not need to be considered when interpreting eye wrinkles, simplifying practical assessment protocols
Key Findings
- •Breed type significantly affected eye wrinkle angle, with thoroughbreds showing the narrowest angle (23.80°), warmbloods intermediate (28.00°), and coldbloods the widest (31.00°)
- •Age, sex, body condition, and coat colour did not systematically affect eye wrinkle expression or assessment in neutral situations
- •Eye wrinkle assessment showed high intra- and inter-observer reliability across five outcome measures
- •Eye wrinkle expression was symmetrical between left and right eyes (p > 0.05)