Peer-reviewed The quality of life of animals is defined by a range of parameters including health, physiology, and behavior. Stress is defined as any damaging strain, force, or agent which stimulates a physiologic defense reaction and is capable under certain circumstances of producing pathologic lesions. Disruption to normal homeostasis can impinge on other biologic processes such as metabolism, cardiovascular activity, immune function, and behavior. In general, chronic stress is considered to have a greater potential impact on animal health and welfare than acute stress, because the animals are exposed and reacting to the stressor(s) for longer periods, thereby causing prolonged disruption to homeostasis and related biologic processes. Impaired coping responses may trigger specific alterations in behavior, organ damage, reduced performance, increased susceptibility to disease, and subfertility. At a molecular level, immune function is mediated by the release of cytokines, nonantibody messenger molecules from a variety of cells of the immune system and from other cells, such as endothelial cells. Biochemical alterations in immune function are, in part, induced by plasma hormone concentration changes elicited by a stressor subsequent to activation of the sympathetic nervous system, the sympathetic adrenomedullary axis, and the hypothalamo–pituitary–adrenocortical axis.
