What is animal stress and how is it measured?

The meaning of the term "stress" as it applies to animal husbandry is discussed. Because "stress" is used with various meanings, its application is often misinterpreted. 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. The correct usage depends upon the school of thought espoused. A common working definition of physiologists is that "stress" consists of external body forces that tend to displace homeostasis and "strain" is the internal displacement brought about by stress. There are environmental forces continuously acting upon animals that disrupt homeostasis, resulting in new adaptations that can be either detrimental or advantageous to man's interest. 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.