lent phrase is “pain, suffering, distress and lasting harm.” Distress can be used to describe a state in which an animal, unable to adapt to one or more stressors, is no longer successfully coping with its environment and its well-being is compromised.

Generally, a state of distress develops over a relatively long period of time; however, short, intense stressor(s) can also compromise animal well-being and induce acute distress. Thus, an animal may be in distress even if it appears to recover rapidly after the removal of the stressor or the conclusion of the procedure.

WHAT IS STRESS?

Stress is an inferred internal state. Because no single biological parameter can adequately inform on a stressful condition and no single stress response is present in all stress-related situations, there are many definitions of stress based primarily on metrics used to test hypothetical models of this state. A general distillation of the literature suggests that stress denotes a real or perceived perturbation to an organism’s physiological homeostasis or psychological well-being. In its stress response the body uses a constellation of behavioral or physiological mechanisms to counter the perturbation and return to normalcy. Events that precipitate stress (called stressors) elicit any of a number of coping mechanisms or adaptive changes, including behavioral reactions, activation of the sympathetic nervous system and adrenal medulla, secretion of stress hormones (e.g., glucocorticoids and prolactin), and mobilization of the immune system. Stress responses may involve at least one and perhaps several of the above systems, although none of them is by itself necessary or sufficient to denote stress. Furthermore, the absence or presence of any of these responses does not include or preclude the identification of a stressful state (for a comprehensive review see Moberg 2000). Stress responses have several key attributes:

  • They serve to promote physiological and psychological adaptation and are, therefore, beneficial and desirable. For example, activation of the sympathoadrenomedullary (SAM) system rapidly increases blood flow to the musculature and raises circulating glucose levels, resulting in an enhanced capacity to flee or fight (the “fight or flight” response). Over a longer time frame, glucocorticoid production in response to infection helps restrict the immune system, thus preventing deleterious effects of inflammatory factors on tissues (Gillis et al. 1979; Munck et al. 1984).

  • Apparent stress reactions can occur in situations unrelated to stress, and therefore their presence alone is not sufficient to indicate stress. For example, the diurnal rhythm of glucocorticoid secretion in most



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