Focussing on vocal expressions of distress, the present study examined vocal responses of 10-week-old domestic pigs during a classical conditioning paradigm, where a neutral light stimulus (conditioned stimulus) was repeatedly followed by a short electric shock (unconditioned stimulus). It is concluded that vocalisation elicited during stressful situations can serve as a differentiated indicator of stressor quality and can be used for the instantaneous assessment of the internal states of pigs.

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