Ear posture, or the frequency of postural changes, may reflect various emotional states of animals. In adult sheep (Ovis aries), the ‘forward’ ear posture has been associated with negative experiences whereas the ‘plane’ posture has been associated with positive ones. This study aimed to see whether ear postures related to the experience of pain in lambs. The ear behaviour of four to eight week-old lambs (n = 44) was measured before and after tail-docking using a rubber ring. Each lamb was docked and its behaviour recorded while in the company of an observer lamb of similar age; each acted once as focal (docked) lamb and once as observer within the same pair. Lambs were docked in one of two rounds, so that half were docked in their first exposure to the test environment and half in their second exposure. Tail-docking was associated with an increase in the proportion of time spent with ears backward and decreases in the proportion of time spent with ears plane and forward (mean [± SEM]: Backward: pre 0.12 [± 0.04], post 0.56 [± 0.04]; Plane: pre 0.55 [± 0.05], post 0.19 [± 0.05]; Forward: pre 0.27 [± 0.04], post 0.18 [± 0.04]). There was also a significant increase in the number of changes between ear postures after docking (pre 5.63 [± 0.66], post 9.11 [± 0.66]). Over both periods, female lambs held their ears asymmetrically for longer than males (mean of ranks [± SEM] [raw proportion of time]: Females 52.14 [± 3.44] [0.09 (± 0.01)], males 37.54 [± 3.40] [0.05 (± 0.01)]). This is the first study to demonstrate changes in the ear posture of lambs associated with the negative experience of pain. Ear posture is a non-invasive indicator of physical pain in lambs and may be useful for evaluating potential welfare compromise.

Given the increased interest in animal emotional reactions for assessing welfare, indicators for such reactions are sought. Ear postures and movements have been found to be promising indicators of emotional states in sheep and other animals. The manual recording of ear postures, however, is very time consuming and possibly prone to a degree of inaccuracy due to the subtle and fast nature of ear movements that have to be identified. Therefore, a number of previous studies have analysed the frequency of certain ear postures relative to all ear posture changes rather than measuring the relative duration spent with different ear postures. Here, we present an automated, continuous tracking system that keeps track of small and lightweight marker balls attached to the head and ears of sheep. We measured ear postures and movements when the animals were confronted with three physical stimuli thought to differ in valence (from negative to intermediate to positive). We then compared new ear-posture definitions reflecting the real time spent with certain ear postures during stimulation with previous definitions used for video-based analyses that assessed ear-posture changes in relation to the total number of observed ear postures. In the analysis, we correlated new and previous measures both between and within experimental stimuli using residuals from mixed-effects models. We found that the new and previous definitions of ear postures and movements correlated highly. Given these high correlations and the discussed theoretical and practical advantages of the automated tracking, the new recording system can be recommended highly for assessing reactions in animals that may indicate emotional states.