Stress early in life may cause changes that will affect an individual its whole life, and it seems that behavioural and cognitive development are particularly sensitive to early experiences. Early life stress has been associated with enhanced emotional and stress reactivity, high levels of aggression and social withd rawal.  Early life stress may be beneficial to the individual, and effects such as a lower sensitivity to stress and enhanced cognitive abilities have ben reported from different studies. Also, studies have suggested that there are different periods during development when an animal is more sensitive to stress than others. 

The objective of this study was to investigate the behavioural short- and long-term effects of stress experienced early in life and during adolescence in the domestic chicken. By treating different groups with a chronic intermittent mild stress paradigm at three different ages, early in life, early adolescence and late adolescence, it was examined whether there are periods during the development into adults when chickens are especially sensitive to stress. In production, chickens are faced with several probable stressors impairing the welfare of the animals, and to identify periods when they are more susceptible to stress might help increase welfare of chickens in production.