Abstract
Identifying valid indicators to assess animals' emotional states is a critical objective of animal welfare science. In horses, eye wrinkles above the eyeball have been shown to be affected by pain and other emotional states. From other species we know that individual characteristics, e.g., age in humans, affect facial wrinkles, but it has not yet been investigated whether eye wrinkle expression in horses is systematically affected by such characteristics. Therefore, the aim of this study was to assess how age, sex, breed type, body condition, and coat colour affect the expression and/or the assessment of eye wrinkles in horses. To this end, we adapted the eye wrinkle assessment scale from Hintze et al. (1) and assessed eye wrinkle expression in pictures taken from the left and the right eye of 181 horses in a presumably neutral situation, using five outcome measures: a qualitative first impression reflecting how worried the horse is perceived by humans, the extent to which the brow is raised, the number of wrinkles, their markedness and the angle between a line through both corners of the eye and the topmost wrinkle. All measures could be assessed highly reliable with respect to intra- and inter-observer agreement. Breed type affected the width of the angle [F(2,114) = 8.20, p < 0.001], with thoroughbreds having the narrowest angle (M = 23.80, SD = 1.60), followed by warmbloods (M = 28.00, SD = 0.60), and coldbloods (M = 31.00, SD = 0.90). None of the other characteristics affected any of the outcome measures, and eye wrinkle expression did not differ between the left and the right eye area (all p-values > 0.05). In conclusion, horses' eye wrinkle expression and its assessment in neutral situations was not systematically affected by the investigated characteristics, except for “breed type”, which accounted for some variation in “angle”; how much eye wrinkle expression is affected by emotion or perhaps mood needs further investigation and validation.
Highlights
Assessing emotional states in animals is a critical goal in animal welfare science, but it is generally agreed that the subjective experience of an emotion cannot be assessed directly [but see [2] for a different point of view]
We aimed to investigate whether eye wrinkle expression in horses is systematically affected by the horses’ individual characteristics age, sex and breed type, since such characteristics might impact the assessment of emotional situations
For the analyses of “breed type” on the different outcome measures, all ponies (n = 7) and the horse without known breed were removed from the data set due to the small sample size, leading to a remaining sample of 916 pictures
Summary
Assessing emotional states in animals is a critical goal in animal welfare science, but it is generally agreed that the subjective experience of an emotion cannot be assessed directly [but see [2] for a different point of view]. Developed for humans, FACSs have been adapted to different animal species, including primates [orangutans [5], macaques [6], chimpanzees [7, 8], gibbons [9]], dogs [10], cats [11], and horses [12]. Besides their application in comparative psychology [e.g., [13]] and research on the evolution of emotional communication [e.g., [14]], FACSs have more recently been used to associate facial expressions with emotional states [11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
