Effects of environmental conditions on the psychological well- being of primates: A review of the literature

Amendments made to the Animal Welfare Act in 1985 require primate researchers to provide "a physical environment adequate to promote the psychological well-being of primates". Regulations have not yet been promulgated, in part because "the psychological well-being" of primates is extremely difficult to define. Ideally, those regulations would be based upon observable changes in behavior rather than assumed psychological changes. Regardless, new primate care regulations pertaining to social environment, cage size, exercise and other forms of environmental enrichment are anticipated. A review of the literature suggests that there is little scientific data to support changing existing regulations. For instance, although it is clear that total social isolation in very young primates can be behaviorally devastating in terms of normal social behaviors, there are few, if any, demonstrable adverse effects of individual housing in adult primates. On the other hand, group housing, particularly with groups changing frequently in composition, increases aggression, trauma and disease transmission. In addition, existing research suggests there are important species differences in terms of social preferences. It is impossible to justify an increase in cage size based upon the available literature. An additional practical consideration is that any change in cage size requirements will necessitate replacement of current primate housing on a national level, an enormously expensive proposition. Regarding environmental enrichment, research suggests that providing a naturalistic environment is not as critical as arranging dynamic events that are contingent upon behavior. However, new research is necessary to specify the types of environmental enrichment that are valuable and appropriate before useless, even damaging, and expensive changes are mandated.