feeding, but providing this may result in prohibitively large spatial and physical demands on 
the research environment. 
SEPARATION FROM THE SOCIAL GROUP 
Questions about social separation will become more common as more research subjects are 
socially housed. Negative impacts of these separations can be minimized. For example, the 
effect of social separation is aggravated by simultaneously placing animals in an unfamiliar 
environment, whereas allowing the animal to remain in the home cage after removal of the 
companion reduces the effects. Similarly, placing the infants with other familiar companions 
reduces the effect of weaning infants from the mother. 
Extensive studies with nonhuman primates have indicated that the largest effects are 
observed in the first day after social separation, although some physiological changes may 
persist for one to two weeks. Both behavioral manifestations of distress and altered 
physiological responses return to normal after this time, and it is often difficult to distinguish 
the animal from its prior social baseline period by overt measures. 
Separation of infant primates from each other at four to six months of age is associated with a 
pronounced behavioral protest reaction (Suomi et al., 1976), but the physiological 
manifestations and effects of separation are by no means as prominent as is the case for 
mother-infant separation (Boccia et al., 1989). Macaques separated from members of their 
nuclear family also exhibit behavioral protest reactions (Suomi et al., 1975), although the 
physiological correlates of such separations have yet to be identified. 
Pair or group housing may be incompatible with some research protocols for some animal 
species. Individual housing may be necessary for animals receiving continual administration 
of experimental diets or drugs, experiments monitoring food and water intake, or experiments 
from which there is regular collection of biological samples. Individual housing may be 
necessary to prevent social companions from handling the research subject's implanted 
instrumentation or attacking the subject while it is recovering from drug treatment. 
Potentially deleterious effects of individual housing can be minimized if carried out in an 
environment that permits visual, auditory, olfactory, and even limited tactile contact. 
Additionally, alternative stimulation and activities can be offered to such subjects during the 
period of restriction. Efforts should be made to minimize individual housing where possible 
in animals previously raised in social environments. Chronicity of the treatment and age ot 
the subject should be evaluated in devising creative alternatives — for example, adjacently 
house two familiar subjects when instrumented or surgically implant the instruments in 
inaccessible locations. Emerging technologies may increase our ability for remote recording ot 
experimental data, further limiting the requirement for individual housing. Physiological 
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