PHYSIOLOGICAL-RESPONSES TO STRESS IN THE HORSE

Stress has been defined as a state in which an animal ''is required to make abnormal or extreme adjustments in its physiology or behaviour i n order to cope with adverse aspects of its environment and management ''. The most common stressors for horses are transport, exercise, lame ness, and environmental temperature and humidity changes. Considerable interindividual animal variation occurs in the endocrine response obs erved subsequent to exposure to these stressors, particularly transpor t and lameness, and indicates considerable variation in individual ani mals' psychological responses to stress. Resting, exercise, and recove ry heart rates have also been shown to be useful indicators of fatigue or lameness. Both exercise and transport have been demonstrated to ha ve considerable effects on pulmonary defence mechanisms and other immu nological functions.