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, 8 (12), e80556

Pain and Pessimism: Dairy Calves Exhibit Negative Judgement Bias Following Hot-Iron Disbudding


Pain and Pessimism: Dairy Calves Exhibit Negative Judgement Bias Following Hot-Iron Disbudding

Heather W Neave et al. PLoS One.

Erratum in

  • PLoS One. 2014;9(4):e96135


Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, but emotional states are difficult to directly assess in animals. Researchers have assessed pain using behavioural and physiological measures, but these approaches are limited to understanding the arousal rather than valence of the emotional experience. Cognitive bias tasks show that depressed humans judge ambiguous events negatively and this technique has been applied to assess emotional states in animals. However, limited research has examined how pain states affect cognitive processes in animals. Here we present the first evidence of cognitive bias in response to pain in any non-human species. In two experiments, dairy calves (n = 17) were trained to respond differentially to red and white video screens and then tested with unreinforced ambiguous colours in two or three test sessions before and two sessions after the routine practice of hot-iron disbudding. After disbudding calves were more likely to judge ambiguous colours as negative. This 'pessimistic' bias indicates that post-operative pain following hot-iron disbudding results in a negative change in emotional state.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Figure 1
Figure 1. Experimental apparatus for training and testing in the judgement bias task.
Calves entered through the front gate to begin each session. The computer controlled the display of positive, ambiguous and negative screens.
Figure 2
Figure 2. Mean ± SE approach responses of calves to each screen colour before and after disbudding.
Calves were trained to approach the positive screen colour for a milk reward, and to avoid approaching the negative screen colour, and were tested with unreinforced ambiguous colours. Calves responded to the ambiguous colours less frequently after versus before disbudding (p = 0.0004); as expected, there was no effect of disbudding on the responses to positive and negative training colours.

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Grant support

This work was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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