Environmental enrichment induces optimistic cognitive biases in pigs

The objective assessment of affective (emotional) state in farm livestock, especially positive states, poses a significant challenge. In human psychology, there is evidence that affective state can alter cognition, with more positive states being associated with an increased likelihood of judging ambiguous information postively (a phenomenon described as optimistic cognitive bias). The aim of this study was to investigate whether judgement biases could be used to assess affective states in pigs housed in environments with different levels of enrichment. Two groups of five gilts were housed in either enriched (E) or barren (B) environments for the first five weeks of the experiment. The enriched group had more space, straw and objects to manipulate. The pigs were trained on a go/no-go task to discriminate two auditory cues, a positive cue that predicted a food reward if the pig approached a hatch, and a negative cue that predicted a mildly aversive experience if the pig approached the same hatch. The quality of the pigs’ environment was then changed over time in a balanced, cross-over design (either EBE or BEB). Tests of cognitive bias were made on individual pigs before and after each change in environment using an unreinforced, ambiguous, auditory cue different from either the positive or the negative cue. In test sessions, positive, negative and amibiguous cues were presented in a randomised sequence, and the pigs’ responses (whether they approached the hatch and latency to approach) were recorded. Both groups were more likely to approach the hatch and were faster to approach the hatch in response to the ambiguous cue when currently housed in the enriched environment. There was also an interaction between current and past environment, whereby pigs that started in the enriched environment were subsequently less likely and slower to approach the hatch when moved to a barren environment than pigs intially housed in the barren environment. These results show that pigs have more optimistic judgement biases in enriched environments indicative of a more positive affective state. Also, pigs that have spent time in an enriched environment react more negatively to being subsequently housed in a barren environment. We conclude that cognitive bias has potential to provide additional information about the effect of various management regimes on farmed animals’ welfare. This will be increasingly important for identifying practices to promote positive affective states in our food producing animals.