Investigation of reward quality-related behaviour as a tool to assess emotions

Animals are likely to appraise events as positive or negative based on their subjective perception, current state and past experiences. We tested the effects of anticipating positive (food anticipation), negative (inaccessible food) and neutral (clicker sound) events on behavioural and physiological responses of 30 goats. The experimental paradigm involved the presentation of a conditioned stimulus (CS) followed by an unconditioned stimulus (US) after a delay. The following parameters were measured at three different time points over 11 test sessions (2 trials / session total of 22 trials): activity, head movements, vocalisations, ear positions, structure of vocalisations produced, and physiological activity. In the positive condition, goats were more active, had increased head movements and call rate, longer durations of ears positioned forward and higher heart rates compared to the other conditions. In the control condition, goats kept their ear backwards for longer compared to the negative condition. No differences were found in vocal parameters and heart-rate variability across conditions. Overall, goats showed different behavioural and physiological responses to positive compared to negative and neutral events, suggesting that the anticipatory response paradigm may be used as a valid tool to capture the affective state of an individual.