Release from restraint generates a positive judgement bias in sheep

The study of judgement biases in animals has attracted interest as a way of potentiallymeasuring emotional states by being able to detect pessimistic-like or optimistic-likeevaluations of their environment. While judgement biases have been successfullyidentified in laboratory species, no such research has been reported in livestock species.Twenty ewes were trained to learn a spatial location task that required a go/no-goresponse according to the location of a bucket in a pen. One bucket location was associatedwith a feed reward, and the other associated with a negative reinforcer (no food and thepresentation of a dog). Ten sheep were then subjected to a 6 h restraint and isolation stress(RIS), for three consecutive days. Following RIS on each day, all sheep were tested forbiases in judgement by measuring their response to three previously unseen bucketlocations and the learnt locations. Serum cortisol, haematological parameters, andbehaviour of the sheep in an open field test were also recorded. Restrained and isolatedsheep were more likely to approach the ambiguous bucket locations compared to controlsheep (P = 0.008), suggesting RIS-treated animals had a more optimistic-like judgementbias. This was despite serum cortisol concentrations showing that sheep were highlystressed by the RIS treatment (P = 0.019). This finding provides evidence that it is possibleto measure judgement biases in a livestock species. When released from RIS the sheep mayhave had a more positive emotional state, or a lesser perception of risk, than that exhibitedby control sheep.