19.09.2022: Some like it hot – but mice don’t. This is the result of a study by the University of Veterinary Medicine Vienna that was recently published in the scientific journal Animals. The study found that higher ambient temperatures have a negative effect on the reproductive outcome of lactating female mice.

Ambient temperature exerts a major influence on the physiology of mice, from heart rate and blood pressure to tumour growth and immunological parameters. The optimal temperature for keeping laboratory mice, however, has been the subject of debate for some time. The current standard temperature is 20 °C to 24 °C. Some researchers have suggested raising the temperature to 30 °C as this is the thermoneutral zone for mice. The argument is that the current temperature range represents a chronic cold stress. The counterargument is that temperatures of 30 °C constitute heat stress.

Higher cage temperature detrimental for mice of all ages

A recently published study by Vetmeduni investigated the effect of different cage temperatures (20 °C, 25 °C, 30 °C) on reproduction and the secretion of stress hormone metabolites in two commonly used mouse strains. The findings show that a higher ambient temperature does not have any beneficial effects for lactating female mice or their young. On the contrary, the number of weaned pups was reduced and both mothers and pups exhibited a lower body weight at 30 °C than at lower temperatures. In addition, the young showed an increased tail length, likely an adaptation to the high temperature.

Recommendation for “cooler” temperature as a standard

The study’s first author, Thomas Kolbe from the Institute for in vivo and in vitro Models at Vetmeduni, summarises further important results of the study: “We did not find any detrimental effects of lower or higher cage temperature on the excretion of stress hormone metabolites in the temperature groups we studied. We did find, however, that reproductive output decreased at the higher temperature.”

Study co-author Kerstin Auer from the Institute for in vivo and in vitro Models at Vetmeduni therefore makes the following recommendation for keeping laboratory mice: “We conclude from our study that the ‘cool’ standard temperature in mouse facilities has no negative effect on animal stress levels, as long as sufficient nest-building material is provided. In consideration of our findings, we cannot recommend a cage temperature of 30 °C for breeding mice.”

The article “Effect of Different Ambient Temperatures on Reproductive Outcome and Stress Level of Lactating Females in Two Mouse Strains” by Thomas Kolbe, Caroline Lassnig, Andrea Pölzl, Rupert Palme, Kerstin E. Auer and Thomas Rülicke was published in Animals.

Scientific article