When individual vertebrates loose grip on their life conditions stress symptoms appear and their welfare becomes problematic. Present day research supports the view that stress can originate when an organism experiences a substantial reduction of predictability and/or controllability (PIC) of relevant events. Behavioural (conflict and disturbed behaviour) and physiological (neuro-endocrine and autonomic processes) aspects of a reduction of PIC are reviewed. The highly dynamic patterns of the homeostatic mechanisms activated during stress make it difficult to deduce any simple relationship between stress and welfare.
A list of relevant stress symptoms has been presented, all of which indicate some stage of serious welfare problems. Their occurrence should never be typical of animals living in a farm, laboratory or zoo housing system. However, if after all this is the case, such systems have to be corrected and replaced by more appropriate ones as soon as possible.
