Stress is a broad term which implies a threat to which the body needs to adjust. Stress may be classified as physical, psychological, or interoceptive in nature, but usually contains components of ail three classifications. The adjustment to stress induces a broad range of neuroendocrine, physiological and behavioural changes to allow for a rapid recovery or adaptation to the change. The hypothalamic-adrenal medullary system involves the hypothalamus, pituitary gland, the sympathetic neural pathways to the adrenal medulla, and the release of epinephrine by the adrenal gland. This short acting stress-response was originally proposed by Waiter Cannon and is referred to as the Fight-Flight Syndrome (FFS). The hypothalamic-pituitary-adrenocortical (HPA) stress-response system with the release of corticosteroids represents a longer-term, sustained response to stressors and was conceptualised by Hans Selye (General Adaptation Syndrome, GAS). These two classical stress response systems have been linked to different coping pattern in that FFS is primarily activated in situations of threat of control, whereas the pituitary-adrenocortical system is activated in situations of loss of control. Several studies have confirmed that unpredictable or uncontrollable stimuli will activate the hippocampal pathway and the HPA axis leading to depression of behaviour. The ability to adjust to some stressors (controllability), however, seems to be under the control of the amygdala through activation of the sympathetic nervous system and prepares the animal for fight and flight responses. In the past, housing systems and handling procedures for farm animals were mainly assessed by descriptive behavioural studies using indicators presumed to be related to stress (i.e,, stereotypic behaviours). Physiological indicators included endocrine changes on the pituitary-adrenal-axis by measuring adrenocorticotropin (ACTH), corticosteroids and catecholamines. The neuroendocrine and immune system has been studied in relation to stress effects at a cellular or neural level during the last decade. Ali these studies were often conducted in an isolated manner without considering that the neuroendocrine and immune system are communicating with each other and are ultimately influenced by the animals individual perception of a stressor. Psychological stressors perceived as threats may be equally important as those of a physical nature in challenging coping mechanisms. Situations of uncertainty, social pressure and fear are potent stressors with relevance for the welfare of animals, leading to severe damage to specific target organs and tissues or even to death in some species. Transportation is considered as a major stressor for farm animals and might have deleterious effects on the health, welfare, performance and ultimately on product quality. Studies on the assessment of stress during animal housing, management procedures and transportation require non-invasive methods as classical approaches of data collection with direct human interference (i.e., for blood collection and heart rate measurement) might directly after the stress response. Telemetric devices for measuring heart and respiration rate, body temperature and blood pressure are useful tools to obtain undisturbed responses. Also, noninvasive measurements of stress indicating metabolites in saliva, faeces or urine has been recently developed and validated. Parallel to behavioural observations, these physiological measurements provide valuable information on coping strategies and the consequences for the welfare of farm animals.
