Abstract : The assessment of farm-animal welfare requires a good understanding of the animals' affective experience, including their emotions. Appraisal theories developed in cognitive psychology provide a conceptual framework to study emotions in animals. It considers emotions to be triggered by a cognitive process where the situation is evaluated according to a limited number of elementary criteria. The emotional experience of an animal can be infered from the likely evaluation it makes in a situation and its subsequent behavioural and physiological responses. It is first necessary to know what criteria animals perceive and whether they influence the emotional response. Knowing the criteria used by a species enables inference to the emotions that individuals could experience. An experimental approach has been developed in lambs to identify the range of elementary criteria used by animals and the specific responses triggered by these criteria. We have shown that lambs evaluate an event to which they are exposed according to the event's predictability, its discrepancy from expectations, the ability of the individual to exert control over it and the social context in which it occurs. This evaluation influences the emotional responses of lambs (behavioural and cardiac). Our characterisation of the criteria used by lambs indicates the kind of emotions they could experience. According to our results, lambs could experience happiness in addition to negative emotions such as fear, anger, disgust, despair, rage and boredom. Further studies to consider combinations of criteria would strengthen these results. Implications of cognitive abilities regarding to animal welfare are discussed.