parameters (Van Loo et al. 2004), while retaining scents in certain areas of the cage (e.g., the top grill) may increase aggression (Gray and Hurst 1995).

Housing animals in groups that are not compatible (e.g., certain strains of postpubertal male mice) can result in aggression, stress, distress, injuries, and even death. While all social groups should be monitored for compatibility, this is particularly important immediately after the formation of the group. Animals that require individual housing may benefit from visual, auditory, olfactory, and even tactile contact with other animals, as such interactions are thought to improve the welfare of all animals involved.

Husbandry

While predictable variations in housing conditions can be a useful component of enrichment, unpredictability in animal care can be stressful and potentially distressing if prolonged or extreme. Even routine cage cleaning and changing can be stressful or become distressful if not consistently and routinely performed in a gentle manner (for more details see Chapter 3). Cardiovascular and behavioral changes, such as elevated blood pressure, heart rate, and movement, lasted up to 60 min after changing the cages of adult male Sprague Dawley rats (Duke et al. 2001). Cage and room cleaning also disrupt olfactory environments that are important to animals that depend on their sense of smell to socialize (Gray and Hurst 1995).

Because husbandry procedures can be stressful to the laboratory animal, performing more than one simultaneously (e.g., weighing animals at the time of transfer to clean cages) may decrease the handling stressor in some species if such arrangements are possible. Alternatively, more frequent, gentle, predictable handling may habituate an animal and thus minimize handling stress. In species such as dogs and primates, strategies such as positive rewards and operant conditioning techniques can minimize stress and thus the potential for distress for both animals and handlers (Prescott and Buchanan-Smith 2003; Weed and Raber 2005). Many techniques that minimize stress in husbandry—such as combining husbandry handling with habituation and handling for research purposes, acclimation to new environments, positive reinforcements, operant conditioning, and well-trained staff—can be helpful tools for the overall reduction of stress and distress; for further information see ILAR Journal 47(4).

It is extremely important to involve both research personnel who are knowledgeable and skilled in current methods and well-trained and attentive animal care employees. Individuals who understand the normal behavior and appearance of animals and have mastered the appropriate handling and restraint techniques are quick to identify abnormal clinical signs that may be indicators of distress. Rapid identification and prompt attention to



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