Evidence links some characteristics of eye wrinkling in horses to different emotional states, researchers report.
Horses display many different facial expressions, with the eyes being highly expressive due to the wrinkles above the eyeball, which some people working with horses use as an indicator of uneasiness or discomfort.
Some horse owners even refer to them as worry wrinkles or worry lines.
Sara Hintze, from the University of Bern in Switzerland, set out with her colleagues to learn what eye wrinkles in horses told us about their emotional state. Could eye wrinkles be used as an easy and non-invasive indicator of a horses’ emotional state?
Hintze told delegates at the recent International Equitation Science Conference in Vancouver, Canada, that, to date, there had not been any scientific study investigating the effect of emotion on the expression of eye wrinkles.
Wrinkles that form above the eye ball within the inner brow area result from the contraction of the underlying inner eyebrow raiser muscles.
Eye wrinkles are common in horses but differ in number and shape between horses and within individuals.
The team of researchers from Switzerland, Britain and the United States asked whether eye wrinkles were caused by negative emotional states in the horse or whether it was simply a case of humans associating wrinkles at the inner eyebrow with worriedness.
The study took place at the Swiss National Stud Farm in Avenches, Switzerland, using 16 horses, most of whom were Franches-Montagnes stallions.
Researchers induced different emotional states in the horses and assessed whether situations presumed to be positive (anticipation of a food reward and petting) would reduce the expression of eye wrinkles, and whether situations presumed to be negative (food competition and waving a plastic bag) would increase it.
All four test conditions were chosen on the basis of being things that horses were reasonably likely to encounter within their regular management system.
During the study a professional photographer captured pictures of both of the eyes of each of the horses’ whilst being tested in all four conditions.
Analysis of the number of wrinkles, the extent of wrinkling and how much white of the eye was shown led to the conclusion that some characteristics of eye wrinkling were affected by different emotional states, Hintze told delegates.
Researchers concluded that emotional states may be linked with characteristics of eye wrinkle expression and may therefore be a potential indicator of horse welfare. However, they indicated that further research was needed.
Hintze was joined in the research by Samantha Smith, from the University of Edinburgh; Antonia Patt, from the University of Maryland; Iris Bachmann, from Agroscope in Switzerland); and Hanno Würbel, from the University of Bern.