LABORATORY ANIMAL MEDICINE AND SCIENCE - SERIES II ...

V-9042 RATS AND MICE: Care and Management 1123. Section title ENVIRONMENTChanges in environmental parameters such as temperature, relativehumidity, and light intensity are known to cause changes in thephysiological reactions of animals and could show up as unwantedexperimental variables in research data. Thus, environmentalparameters should be kept as stable as possible within normal ranges.24. Physical The environmental parameters in a room (macroenvironment) may bevery differentconditions from those within an animal cage (microenvironment). Thus, the designand use of caging—suspended wire versus shoebox cage with filtertop, the number of animals per cage, the total animal population withina room, the humidity within the cage and the room, and the number ofair changes per hour can affect environmental conditions.25. Temperature The Guide recommends room temperatures for rats and mice in arange of 18 to26_C (64-79_F) (2). Room temperature can be monitored and adjustedby sophisticated electronic monitoring systems or evaluated by use ofmaximum-minimum thermometers located in each animal room.Environmental temperatures outside these accepted ranges can affectreproductive performance, food consumption, and metabolism of testagents. Rats and mice can produce significant heat depending onventilation within the cage and the cage population, so cagemicroenvironmental temperatures can exceed recommended ranges.Where LAF or other systems with high rates of air exchange areutilized, temperatures within and around the cages may decrease, andchilling of animals, especially nude mice, may occur.26 HumidityRecommended relative humidity (RH) for rats and miceshould be maintained in a range of 30 to 70% (2). Asillustrated in this image, RH can be measuredelectronically and monitored centrally in facilities withmodern air handling systems, or it can be monitoredwith a hygrothermograph chart recording device placedin a room. Undesirably high humidity may be caused byexcessively wet bedding, rooms containing racks withautoflush waste pans, and low room air exchange rates.High air flow rates and heated air during winter monthscan cause the RH to drop below desired levels.27. High or low RH High humidity, coupled with an elevated room temperature, can lead toheat stress and reduced resistance to infections in rats and mice (4).Low humidity results in increased accumulation of dust in animal cagesand rooms--dust that can transport viral and bacterial agents. Lowhumidity can also decrease the function of the mucociliary apparatus inthe respiratory passages, allowing particulate matter to accumulate inthe lungs, predisposing the animal to pneumonia and other respiratoryillnesses.