volume of space and opportunity to express species-typical behavior, may be used …" That statement and paragraph 3.81(a) (Social Groupings) properly encourage social groupings and behaviorally defined cage space. However, many nonhuman primates are now singly housed because of paragraph (b)(2)(iv) which states that: "when more than one nonhuman primate is housed in a primary enclosure, the minimum space requirement for the enclosure is the sum of the minimum floor area space required for each individual nonhuman primate…." We believe that the latter statement is indefensible and that cage design (volume and furnishing) should result from a thoughtful understanding of the needs of the animals, not from multiples of body weight of the inhabitants. We further believe that many nonhuman primates in single cages today would benefit from a compatible cagemate, even if the cage sizes do not precisely meet the letter of the law (Eaton and others 1994; Reinhardt and Hurwitz 1993); such is the strength of our belief in the value of social housing. This attitude is also expressed in the Guide for the Care and Use of Laboratory Animals (NRC 1996).

Providing housing environments with materials, surfaces, and structures that support species-normal activities might make them more difficult to sanitize. For example, the use of wood shavings and wooden structures has often been discouraged in primate enclosures for sanitation reasons. However, at least one study (Chamove and others 1982) has found a decrease in bacterial content over time in wooden shavings placed on the cage floor and an increase in behavior classified as desirable in five of six species of nonhuman primates studied. Some natural wood products contain bactericidal compounds that provide self-sanitation (D.O. Cliver, University of Wisconsin-Madison, unpublished data, 1993). Straw or woodchip bedding, ropes of natural materials, branches, and cardboard products can all increase the variety of surfaces and objects in a cage. When these materials have been replaced because of wear or soiling, they have not been found to constitute a health hazard. The colony manager, veterinarian, and institutional animal care and use committee (IACUC) should monitor the effectiveness of these cage modifications to ensure they enhance well-being consistent with good sanitation and the requirements of the research project. (See also NRC 1996.)

Although chewed wooden structures might not be aesthetic, some species need to chew wood or other suitable material to keep their teeth and gums in good condition. Other species require wooden or porous surfaces for scent-marking (Epple 1986). The use of wooden structures and objects to support locomotor and manipulative activity should require only that appropriate schedules be developed for replacement to meet valid sanitation concerns. Likewise, open water in streams, pans, or puddles supports varied activities in many species and should be acceptable, given reasonable procedures to maintain sanitation. The frequency of changing soiled or worn materials and access to streams or puddles requires reasonable care to ensure that they do not present a health hazard. Access to streams or puddles need not be routinely prevented (NRC 1996, p. 41).

Those who develop plans for psychological well-being and those evaluating

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