Warmer is better

Mice are not humans. Mice and humans differ strongly in body size and mice lose energy and heat at a faster rate than humans. The choice of housing temperature is typically dictated by the comfort of laboratory personnel but it is not necessarily comfortable for mice that spend their entire life in these environments and our mice are likely to experience chronic cold stress in their boxes. So let’s listen to what mice can tell us about good thermal conditions.

The standard narrow range temperature usually varies from 20 to 24ºC in breeding facilities, even though if in practice mice are often housed in a range of 20 to 22ºC. In addition, individually ventilated cage systems may increase the sensation of cold, especially when ventilation cycles are shorts. Yet, the mouse thermoneutral zone in which the metabolic rate is minimal is comprised between 28 and 34ºC. When given the choice, mice prefer temperatures comprised between 25 and 30ºC over 20ºC. Females that are more skittish, also strongly prefer 30 over 25ºC.

mice_cold stress

Photo credit: https://www.commons.wikimedia.org/wiki/File

Beyond the undoubtable effects on welfare, cold environments are stressful, and can therefore affect pup survival as well as mouse physiology and behaviour. Isolated mouse pups spend much of their time emitting distress calls when the temperature is below 27ºC while they rarely call above 33ºC. In adults, the metabolism and food consumption roughly increase of 50% when mice are raised at 22ºC instead of 30ºC. Evidence show that mice are hypertensive, sleep-deprived, obesity-resistant, fever-resistant, aging-resistant and are more susceptible to cancer and infections at temperatures below their thermoneutral zone.

These actual failures to listen to the captive animals always make me think about to what extent scientific results are valid and translating to human biology research?

Of course, like in humans, there is no one optimum temperature for all animals since preference differs between sex, strain, type of activity, and moment of the day. For example, although 32ºC may be ideal for sleeping, mice may experience a heat stress when running in a wheel or climbing the feeder. It makes difficult to select a single housing temperature adequate for all mice. The nesting material supply and group-housing are alternatives to compensate for low cage temperature. They allow animals to insulate themselves when they want, especially during inactive period during which metabolic heat generation is reduced. Having the choice (to choose the good temperature, for example) is an important factor for living beings. However, we should not forget that microenvironment inside the cage may only compensate for 1.8ºC and turning up the heating at 25-27ºC may still be necessary to improve mice comfort and welfare and increase scientific validity in research.

Sources:

David, J.M., Knowles, S., Lamkin, D.M., Stout, D.B., 2013. Individually ventilated cages impose cold stress on laboratory mice: a source of systemic experimental variability. Journal of American Association for Laboratory Animal Science 52:6, 738-744.

Gaskill, B.N., Gordon, C.J., Pajor, E.A., Lucas, J.R., Davis, J.K., Garner, J.P., 2013. Impact of nesting material on mouse body temperature and physiology. Physiology & Behavior 110-111, 87-95.

Gaskill, B.N., Rohr, S.A., Pajor, E.A., Lucas, J.R., Garner, J.P., 2009. Some like it hot: Mouse temperature preferences in laboratory housing. Applied Animal Behaviour Science 116, 279-285.

Maher, R.L., Barbash, S.M., Lynch, D.V., Swoap, S.J., 2015. Group housing and nest building only slightly ameliorate the cold stress of typical housing in female C57BL/6J mice. American Journal of Physiology. Regulatory, Integrative and Comparative Physiology 308, R1070-R1079.

Maloney, S.K., Fuller, A., Mitchell, D., Gordon, C., Overton, J.M., 2014. Translating Animal Model Research: Does it matter that our rodents are cold? Physiology 29, 413-420.

Okon, E.E., 1970. The effect of environmental temperature on the production of ultrasounds by isolated non-handled albino mouse pups. Journal of Zool Lond 162: 71–83.

Toth, L.A., Trammel, R.A., Ilsley-Woods, M., 2015. Interactions between housing density and ambient temperature in the cage environment: Effects on mouse physiology and behavior. Journal of the American Association for Laboratory Animal Science 54:6, 708-717.

Sophie B.

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