Cognitive bias tests in pigs measure optimistic or pessimistic judgment that reflects underlying emotional states, providing objective indicators of positive and negative welfare.
Cognitive bias testing represents a significant methodological advance in assessing pig welfare because it provides evidence of subjective emotional states rather than just behavioral outputs. A pig showing pessimistic bias is experiencing a negatively valenced emotional state that constitutes genuine welfare harm regardless of whether overt suffering behaviors are visible. The finding that enrichment reliably shifts pigs toward optimistic bias provides strong experimental support for the welfare value of environmental improvement. These methods are moving the field toward objective measurement of positive welfare rather than only absence of suffering, enabling more nuanced welfare assessment and comparison between production systems.