The biology of stress and its application to livestock housing and transportation assessment

Stress is a broad term that implies a threat to which the body needs to adjust. Stress can be classified as physical, psychological, or interoceptive in nature but usually contains components of all three classifications. The adjustment to stress induces a broad range of physiological and behavioral changes that allow for a rapid recovery or adaptation to the change. In the past, housing systems and handling procedures for farm animals were mainly assessed by descriptive behavioral studies using indicators presumed to be related to stress (i.e., stereotypic behaviors). Physiological indicators included endocrine changes of the pituitary-adrenal-axis by measuring ACTH, corticosteroids, and catecholamines. The neuroendocrine and immune systems have been studied in relation to stress effects at the cellular or neural level during the last decade. All these studies were often conducted in an isolated manner without considering that the neuroendocrine and immune systems are communicating with each other and are ultimately influenced by the animals' individual perception of a stressor. Transportation is considered a major stressor for farm animals and might have deleterious effects on health, well-being, performance, and, ultimately, product quality. Studies on the assessment of stress during animal transportation require noninvasive methods because classical approaches of data collection with direct human interference (i.e., for blood collection and heart-rate measurement) might directly alter 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, feces, or urine have been developed and validated. Parallel to behavioral observations (via video recordings), these physiological measurements provide valuable information on how livestock handling and transportation can be improved in the near future.