Welfare by the ear: comparing relative durations and frequencies of ear postures by using an automated tracking system in sheep

Abstract

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.

Frontal Brain Activity and Behavioral Indicators of Affective States are Weakly Affected by Thermal Stimuli in Sheep Living in Different Housing Conditions

“…Ear postures and movements as indicators of emotions ( 3 , 4 , 12 – 14 ) were measured by an automatic tracking system (TrackPack4, Advanced Realtime Tracking GmbH, Weilheim, Germany) consisting of four infrared cameras located in the four top corners of the test pen, a head target (four connected reflective marker balls fixed by a halter on the top of the head between the ears, 142 g), and two single reflective marker balls [fixed by a screw on the backside of the earmarks of both ears, 2.6 g; for more detailed information see Ref. ( 33 )]. We distinguished between four different ear postures, all calculated as a proportion of time and for each single repetition of the stimuli: forward ears (both ears pointed more than 0 degrees forward), backward ears (both ears pointed more than 10 horizontal degrees backward), passive ears (both ears more than 30 vertical degrees below horizontal), and left ear forward (left ear positioned more than 5 horizontal degrees more forward than right ear per all ear positions with more than 5 degrees difference in their horizontal angle).…”

“…All animals at Agroscope, Tänikon, are considered farm animals and are kept according to the relevant regulations of the Swiss Animal Welfare law. The sheep used in the current experiment were purchased as lambs from two sheep dairy farms and they were used in several experiments of a larger project ( 3 , 4 , 28 , 33 ). At the end of the project, the sheep were again sold to a working farm.…”

Housing conditions influence cortical and behavioural reactions of sheep in response to videos showing social interactions of different valence

“…Ear movements and postures were recorded during the test by an automatic tracking system (Trackpack4, Advanced Realtime Tracking GmbH, Weilheim, Germany; [12,15]). This system was based on four infrared cameras covering the test pen and tracking small reflective marker balls in 3D.…”

“…The ear targets were fixed singly at the backside of each ear on the earmarks and could be located in absolute 3D space. Based on this data, we calculated the relative position of the ears in relation to the head as expressed by forward/backward and vertical angles at 6 Hz (further details described in [12,15]). …”

“…While humans can express their subjectively perceived emotions verbally, indicators are needed to assess emotional states in animals [9,10]. Locomotor activity [11], restlessness behaviour [12], and ear postures and movements [11][12][13][14][15] have been used as behavioural indicators of animal emotions in recent studies. These studies related increased locomotor activity and restlessness behaviour with negative stimuli.…”