The accurate measurement of emotional or affective states in animals is a key goal in animal welfare science. Although we may never know for sure whether other species are able to consciously experience such states and, if so, which species do, we can develop methods for indirectly measuring these states.

A new approach instigated by animal welfare scientists draws on the finding from human psychology that a person’s emotional state or mood affects how they think and make decisions.

Depressed or unhappy people are more likely to judge ambiguous things negatively – for example, they will interpret a phrase such as ‘the doctor measured little Emily’s growth’ in a negative way – compared to happier people. The development of a novel decision-making task for animals has allowed animal welfare researchers to show that animals in a negative affective state also exhibit negative or ‘pessimistic’ changes in decision-making. Changes in decision-making may therefore be used as a new measure of animal emotional states, and hence welfare. This new approach has been picked up and used in other disciplines such as neuroscience.