Whereas physiological and behavioural responses to acute stressors are well documented, chronic stress remains difficult to assess in farm animals. The aim of the present paper is to investigate whether calves' behavioural reactions to acute events are modified during chronic intermittent
stress. Thirty-two calves housed in pairs were used. For half of the calves the partner and the pen were changed once a week for 14 weeks (regrouped calves) while the others remained unchanged (controls). Four behavioural tests were performed to assess calves' reactivity to novel or sudden
events, to predator cues and to restraint. In the water spray test, regrouped calves were startled more often. In the umbrella test, regrouped calves took a longer time to feed in front of the closed umbrella but no differences between the two treatments were observed on opening the umbrella.
In the dog test, regrouped calves moved more and looked at the dog more often. In the restraint test, regrouped calves were more agitated. These differences disappeared when the tests were repeated. In conclusion, repeated changes in the social and physical environment of calves enhances their
behavioural reactivity to novelty. This is likely to make them more adaptive to potential changes in their environment.