Tamioso, P. R., Maiolino Molento, C. F., Boivin, X. et al. 2018. Inducing positive emotions: Behavioural and cardiac responses to human and brushing in ewes selected for high vs low social reactivity. Applied Animal Behaviour Science 208, 56-65.
Welfare concerns not only the absence of negative emotional experiences but also the presence of positive experiences. However, scientific investigation on positive emotions in farm animals has been long neglected. This study aimed to investigate the perception of sheep to positive stimuli and whether emotional reactivity influences such perception, through behavioural and cardiac indicators. Therefore, 38 Romane ewes belonging to two divergent lines, high (R+) or low (R−) reactive, were submitted to the presence of a familiar experimenter (HUM) or brushing by a familiar experimenter (BRU). The procedure was divided in three phases: before (2.5 min), during (3.0 min) and after (2.5 min) HUM or BRU. Body postures, head orientation, ear changes and postures, closed and half-closed eyes, tail wagging and feeding behaviour were analyzed, and heart rate variability parameters (RMSSD, RMSSD/SDNN and LF/HF ratios) were estimated. Data were analyzed using linear models with different correlation structures. The models considered treatment, genetic line and phase as fixed effects, including their interactions. Brushed ewes showed fewer body posture, head orientation and ear posture changes and a higher proportion of closed and half-closed eyes, tail wagging and rumination during the procedure, when compared to ewes submitted to the human presence (P < 0.05). Both BRU and HUM ewes had lower HR during and after the procedures and higher RMSSD/SDNN rate during the procedures, reflecting the activation of the parasympathetic nervous system in response to both treatments (P < 0.05). Behavioural and cardiac results suggest that both treatments induced a relaxing state in sheep, more pronounced for the brushing treatment. Interestingly, an anticipatory agitation before the treatment was observed mainly in BRU sheep. Highly reactive ewes expressed less head orientation changes and a higher proportion of horizontal ear postures and feeding behaviour in response to brushing than when submitted to human presence (P < 0.05), indicating that brushing might have elicited a more relaxing effect on R+ animals. Differences between R+ and R− ewes suggest that reactivity might modulate sheep responses to assumed positive stimuli.