Guide for the Care and Use of Laboratory Animals - Office of ...

ENVIRONMENT, hOUSING, ANd MANAGEMENT 43Temperature and humidityMaintenance of body temperature within normal circadian variationis necessary for animal well-being. Animals should be housed within temperatureand humidity ranges appropriate for the species, to which they canadapt with minimal stress and physiologic alteration.The ambient temperature range in which thermoregulation occurs withoutthe need to increase metabolic heat production or activate evaporativeheat loss mechanisms is called the thermoneutral zone (TNZ) and is boundedby the lower and upper critical temperatures (LCTs and UCTs; Gordon 2005).To maintain body temperature under a given environmental temperatureanimals adjust physiologically (including their metabolism) and behaviorally(including their activity level and resource use). For example, the TNZof mice ranges between 26°C and 34°C (Gordon 1993); at lower temperatures,building nests and huddling for resting and sleeping allow them tothermoregulate by behaviorally controlling their microclimate. Althoughmice choose temperatures below their LCT of 26°C during activity periods,they strongly prefer temperatures above their LCT for maintenance and restingbehaviors (Gaskill et al. 2009; Gordon 2004; Gordon et al. 1998). SimilarLCT values are found in the literature for other rodents, varying between26-30°C for rats and 28-32°C for gerbils (Gordon 1993). The LCTs of rabbits(15-20°C; Gonzalez et al. 1971) and cats and dogs (20-25°C) are slightlylower, while those of nonhuman primates and farm animals vary dependingon the species. In general, dry-bulb temperatures in animal rooms shouldbe set below the animals’ LCT to avoid heat stress. This, in turn, means thatanimals should be provided with adequate resources for thermoregulation(nesting material, shelter) to avoid cold stress. Adequate resources for thermoregulationare particularly important for newborn animals whose LCT isnormally considerably higher than that of their adult conspecifics.Environmental temperature and relative humidity can be affected byhusbandry and housing design and can differ considerably between primaryand secondary enclosures as well as within primary enclosures. Factors thatcontribute to variation in temperature and humidity between and withinenclosures include housing design; construction material; enrichmentdevices such as shelters and nesting material; use of filter tops; number,age, type, and size of the animals in each enclosure; forced ventilation ofenclosures; and the type and frequency of contact bedding changes (Besch1980).Exposure to wide temperature and humidity fluctuations or extremesmay result in behavioral, physiologic, and morphologic changes, whichmight negatively affect animal well-being and research performance aswell as outcomes of research protocols (Garrard et al. 1974; Gordon 1990,