by human assessors, the scientific literature supports few engineering standards. This report emphasizes science-based performance standards, which define an outcome (such as animal well-being or safety) and provide criteria for assessing that outcome without limiting the methods by which to achieve that outcome (NRC, 1996). The use of performance standards allows researchers and shippers the flexibility to adjust their procedures to optimize animal welfare on the basis of the species being transported, the mode of transportation, and local environmental conditions.
Although the word stress generally has adverse connotations, stress is a familiar aspect of life—a stimulant for some, a burden for others. Numerous definitions have been proposed for stress. Each definition focuses on aspects of an internal or external challenge, disturbance, or stimulus; on perception of a stimulus by an organism; or on a physiological response of the organism to the stimulus (Goldstein, 1995; Sapolsky, 1998; Selye, 1975). An integrated definition states that stress is a constellation of events including a stimulus (stressor), a reaction in the brain precipitated by the stimulus (stress perception), and an activation of the body’s physiological fight or flight systems (stress response) (Dhabhar and McEwen, 1997). Transportation stressors can be physical (changes in temperature, humidity, or noise), physiological (limitation of access to food and water), and psychological (exposure to novel individuals or environments).
It is important to recognize that stress does not always have adverse consequences (Dhabhar and McEwen, 2001; Pekow, 2005), and it is often overlooked that a stress response has healthful and adaptive effects (Dhabhar and McEwen, 1996; McEwen, 2002).
Stress can be harmful when it is long-lasting and animals are unable to adapt successfully to it (Dhabhar and McEwen, 1997; Irwin, 1994; Kiecolt-Glaser et al., 2002; McEwen, 2002); therefore, an important distinguishing characteristic of stress is its duration. Acute stress is defined as stress that lasts for minutes, hours, or a few days; and chronic stress as stress that persists for months or years (Dhabhar and McEwen, 1997; McEwen, 2002). Most transportation events last only a few days and are considered acute stress events. Even the transportation of animals from overseas does not take more than a few days, so there is little concern about chronic stress during transportation. However, care must be taken to minimize post-trip stress in order to ensure that animals are not chronically stressed.
Transportation of animals involves three phases or periods: pretrip, intermodal, and post-trip. During the intermodal period, trip time has a large effect on the stressfulness of the experience. Animals experience a