The detection of judgement biases may improve welfare evaluations by measuring thecognitive component, particularly the valence, of affective states. Judgement biases havebeen successfully demonstrated in various laboratory animals but only recently in sheep.Chronic stressors have been found to induce a negative judgement bias and a short-termstressor (restraint and isolation stress) a positive judgement bias. Here we examine theimpact of the short-term stress of shearing on judgement bias, haematology, plasma cortisoland stress-induced hyperthermia (SIH) in sheep. Twenty-four Merino ewes weretrained to spatially differentiate between positive and negative reinforced bucket locationswith a go/no-go approach response. Judgement bias was tested by offering sheepthree ambiguous, unreinforced bucket locations and the learnt locations. The responseof the shorn sheep (n = 12) was compared to that of the control sheep (n = 12) with twocohorts of sheep tested on consecutive days. Following the analysis of the core temperature(SIH) responses, a subsequent study was performed to determine SIH to shearing withoutjudgement bias testing. The cohortÃ—treatmentÃ—bucket location interaction approachedsignificance (P = 0.056). In cohort 1, shorn sheep displayed a more positive judgement bias,approaching the ambiguous bucket locations more than the control sheep (P = 0.033). Howeverthere was no difference in judgement bias in cohort 2 (P = 0.908). Decreased eosinophilcount (P'0.001), increased plasma cortisol concentration (P'0.001) and stress-inducedhyperthermia (P'0.001) in the shorn sheep all confirm that shearing was an acute stressor.This study suggests that sheep display a more positive judgement bias following releasefrom shearing. This could reflect a more optimistic affective state induced by release from anacute stressor, oran altered risk perception. These findings support previous studies whichsuggest that testing judgement bias is a possible method for determining the cognitivecomponent of affective state in sheep.
Sanger, M. E., Doyle, R., Hinch, G. N., & Lee, C. (2011). Sheep exhibit a positive judgement bias and stress-induced hyperthermia following shearing. Applied Animal Behaviour Science, 131(3-4), 94-103. https://doi.org/10.1016/j.applanim.2011.02.001