Do judgment biases and emotional reactivity reflect the mental state of sheep?

Abstract

Assessment of mental state is an important goal in animal welfare. The mental states of animals have been assessed using judgement bias but not in livestock. There is also the possibility that emotional arousal (emotional reactivity) could be indicative of mental state. This study aimed to induce differences in the mental states of sheep and then determine if this altered their judgement biases and emotional reactivity. To test for judgement biases, twenty-six ewes were trained to respond to two different bucket positions in a 3x6 m pen. One position was positively reinforced with food so the sheep approached it quickly; the other was associated with a fan-forced blower so the sheep avoided it. Following training, half the sheep were subjected to unpredictable, aversive events (2-3 per day for 3 weeks) that might modify mental state while control sheep were maintained in a standard environment. Events included restraint, mixing with unfamiliar sheep, exposure to a dog, simulated shearing, ear tattooing, foot bathing and transportation. Treated and control sheep were then tested for judgement biases by presenting the bucket in ambiguous locations between the learned positions, and responses were recorded.