Changes in plasma Cortisol concentrations in response to a stimulus have been used to indicate aversiveness. Hormone concentrations at any time point depend on the interaction between an animal's previous experience and its present physiological state. In order to assess how an animal's perception of, and thus its response to, a stimulus change as it gains experience of the stimulus, eight Welsh Mountain ewes were subject to 2h road transport daily on three occasions and then once again 4 days later. Differences in Cortisol concentrations in plasma samples taken every 15min were assessed using a general linear model and Tukey's test.