quences of stress. Many studies have used electric shock as a stressor and have examined the effects of predictable vs. unpredictable electric shock and of providing animals with the means of escaping or avoiding shock or having control over it. The effects of novelty have been investigated by placing animals in wholly unfamiliar settings or presenting new stimuli in familiar settings. In general, novelty, the absence of predictability, and the lack or loss of control cause an increase in the activity of stress-responsive physiologic systems (Hennessy and Levine, 1979; Weinberg and Levine, 1980). Similarly, the human handling of most animals reduces anxiety and fear, but the handling of animals unaccustomed to it can be a profound stressor (Gäartner et al., 1980). In that regard, it is wise to follow practices established by the institution or the research protocol in order to minimize stress in the animals and reduce variability between them.
Many of the conditions that have been shown to be stressful in experimental research have parallels in common colony management procedures. Changing cages, confinement in a strange setting, physical restraint, venipuncture, injections, and modifications of established maintenance routines are examples of events that confront animals with novelty, unpredictability, and loss of control and that are potentially stressful. The magnitude and duration of the stressful effects of those events are influenced by many factors, including the number of previous exposures an animal has had to the particular conditions, its early experience, its temperament, and the skill and sensitivity of the persons carrying out the procedures.
Predictability and a sense of control over research environments can be provided by enabling animals to adapt to novel environments. Adaptation is particularly important before animals are placed on experimental protocols that require restraint, for example. Letting dogs adapt to people through a process of socialization at appropriate ages and frequencies serves a similar purpose and reduces the fear and anxiety that might occur when they are approached or restrained by people.
Transportation has long been known to cause stress in animals. Whether the stress is due to alterations in circadian rhythms, changes in familiar surroundings, noise and vibration, extreme temperature, dehydration, or some other cause is not known. However, standard practices should be implemented to ensure that transportation to and with a research institution follows accepted procedures and that newly arrived animals are given enough time to recover and to adapt to the new environment before they are placed in an experiment (Landi et al., 1982). Scheduling of direct flights, provision of enough food and water and of ventilation, and avoidance of extremes in temperatures to which the animals have not adapted are essential.
Boredom is the response to the opposite of excessive novelty and unpredictability. It is caused by too little variety and change. The immediate surroundings of many captive animals seem barren, unchanging, and nonstimulating. Few things provoke their attention or maintain their interest, and they can do little to relieve the apparent monotony of the situation.