Abstract

Behavioural and physiological markers of discrete positive emotions remain little investigated in animals. To characterise new markers in horses, we used tactile stimulations to induce emotional situation of contrasting valence. In the Gentle grooming group (G, N = 13) horses were gently groomed during 11 sessions on the body areas they appreciated the most. Horses in the Standard grooming group (S, N = 14) were groomed using a fixed procedure, reported to induce avoidance reactions in some horses. At session 11, G horses expressed significantly more contact-seeking behaviours than S horses, which expressed significantly more avoidance behaviours. This result suggests positive emotions in G horses and negative emotions in S horses. Blood cortisol, oxytocin, heart rate and heart rate variability never differed between before and after the grooming session. However, after the 11 sessions, basal oxytocin levels were lower in the G than in the S group. This difference was unexpected, but supports studies showing that a low level of basal oxytocin could be a marker of better well-being. Analyses of facial expressions during grooming revealed significant differences between groups. These expressions appear to be more sensitive than behavioural indicators because they alone enabled differentiating emotions according to the group when horses were re-exposed to neutral grooming one year after the treatment.

Highlights

  • The study of animal emotion is a field of research that has developed considerably in recent years

  • This study aimed to apply two contrasting situations in terms of emotional valence and to determine whether they were associated with specific behaviours, facial expressions and physiological responses

  • Groups were mainly represented on Factor 1 (41.80% of the total variability), with S horses mainly distributed on the left side and G horses on the right side

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Summary

Introduction

The study of animal emotion is a field of research that has developed considerably in recent years. This study aimed to apply two contrasting situations in terms of emotional valence and to determine whether they were associated with specific behaviours, facial expressions and physiological responses (cortisol, oxytocin, heart rate and heart rate variability). We controlled the type of inductive stimulation by focusing only on somatosensory stimulation: tactile contacts This type of stimulation (stroking, grooming, brushing, scratching, etc.) is interesting to study because it can generate opposite emotional responses depending on its characteristics, which can be expressed either by avoidance (cows38,39) or by positive responses such as contact seeking or a relaxed state (sheep[3,40]; cattle[39,41]; heifers[42]; dogs[43]; horses[15,30,44]). If grooming procedures impact valence and not arousal, we would expect no change in heart rate or heart rate variability

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