can influence the results. Water can be treated or purified to minimize or eliminate contamination when protocols require highly purified water. The selection of water treatments should be carefully considered because many forms of water treatment have the potential to cause physiologic alterations, reduction in water consumption, changes in microflora, or effects on experimental results (Fidler 1977; Hall et al. 1980; Hermann et al. 1982; Homberger et al. 1993; NRC 1996).

Watering devices, such as drinking tubes and automated water delivery systems, should be checked frequently to ensure appropriate maintenance, cleanliness, and operation. Animals sometimes have to be trained to use automated watering devices and should be observed regularly until regular usage has been established to prevent dehydration. It is better to replace water bottles than to refill them, because of the potential for microbiologic cross contamination; if bottles are refilled, care should be taken to return each bottle to the cage from which it was removed. Automated watering distribution systems should be flushed or disinfected regularly. Animals housed in outdoor facilities may have access to water in addition to that provided in watering devices, such as that available in streams or in puddles after a heavy rainfall. Care should be taken to ensure that such accessory sources of water do not constitute a hazard, but their availability need not routinely be prevented. In cold weather, steps should be taken to prevent freezing of outdoor water sources.

Bedding and Nesting Materials Animal bedding and nesting materials are controllable environmental factors that can influence experimental data and improve animal well-being in most terrestrial species. Bedding is used to absorb moisture, minimize the growth of microorganisms, and dilute and limit animals’ contact with excreta, and specific bedding materials have been shown to reduce the accumulation of intracage ammonia (Perkins and Lipman 1995; E. Smith et al. 2004). Various materials are used as both contact and noncontact bedding; the desirable characteristics and methods of evaluating bedding have been described (Gibson et al. 1987; Jones 1977; Kraft 1980; Thigpen et al. 1989; Weichbrod et al. 1986). The veterinarian or facility manager, in consultation with investigators, should select the most appropriate bedding and nesting materials. A number of species, most notably rodents, exhibit a clear preference for specific materials (Blom et al. 1996; Manser et al. 1997, 1998; Ras et al. 2002), and mice provided with appropriate nesting material build better nests (Hess et al. 2008). Bedding that enables burrowing is encouraged for some species, such as mice and hamsters.

No type of bedding is ideal for all species under all management and experimental conditions. For example, in nude or hairless mice that lack eyelashes, some forms of paper bedding with fines (i.e., very small particles found in certain types of bedding) can result in periorbital abscesses (White

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