biostudies-literatureUnknown6Schanz LIdentifying 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 eyFrontiers in veterinary science154https://www.ebi.ac.uk/biostudies/studies/S-EPMC6549476biostudies-literatureSex and Age Don't Matter, but Breed Type Does-Factors Influencing Eye Wrinkle Expression in Horses.PMC6549476Hintze SKrueger KSchanz LfalseSex and Age Don't Matter, but Breed Type Does-Factors Influencing Eye Wrinkle Expression in Horses.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 ey2019-01-01T00:00:00Z20192025-04-04T12:15:23.491Z2019-07-24T07:10:08ZS-EPMC65494763119223510.3389/fvets.2019.00154