Animal impacts: distress
Clark J. Does distress matter? AATEX 2008; 14(Spl. Issue): 93-5.
Link to article

ABSTRACT
Most individuals engaged in modern animal based research recognise the importance of pain both as a factor impacting animal welfare as well as a contributor to experimental variability. Less widely recognised is the role of distress, particularly that which is unassociated with pain, in both these respects. Stress is widely considered to be an important factor in an animal's ability to respond effectively to its environment. However, when the animal becomes unable to adapt completely to stressors, and manifests abnormal physiological or behavioural responses, we recognise this as distress. This paper considers the definition of distress, and the ways in which animals mount biological responses to deal with distress. It is very difficult to precisely measure distress which is one reason why it may often be ignored. However the signs are recognizable to the experienced eye. Furthermore, a range of devices can be employed to minimise the level of distress which an animal may experience during a procedure.