Some problems with the physiological concept of "stress".

Stress has become a central concept in discussion of animal welfare, partly because it has been seen to have a precise physiological definition. However, stress is a term in ordinary language with a variety of connotations, not all of which can be related to activity of the pituitary adrenal axis. There is good evidence against the idea that the rise in plasma corticosteroids that occurs in response to some treatment can be used to assess the degree of suffering or distress experienced by an animal. The rise may simply reflect demands on the learning abilities of the animals. Veterinarians should be careful in their use of the term, and in their interpretation of such physiological data, in the context of animal welfare.