Stress in general is looked upon as a symptom resulting from exposure of an animal to a hostile environment. To some it is a nonspecific response to all environmental forces; others feel there are specific stress symptoms caused by specific environmental forces. The term stress is sometimes used to describe the hostile environment. Measuring the magnitude of stress often means measuring the degree of adaptation. The important function of livestock management is to avoid the detrimental adaptations and capitalize on the advantageous ones. Animal Welfare, Behavior and Stress are biological measures of stress. Animals cn be used as models of PTSD, Depression and other diseases.