Reducing Environmental Stress For Laboratory Mice

Stress is an animal’s natural bodily response to a situation that they are unable to cope with, and many animals in laboratories experience stress from their living environment. While animals in the wild can make moves and try to avoid stress or escape stressful situations, animals in labs do not have the same options. This study investigated which environments cause the least stress to laboratory mice.

Researchers looked at three environmental variables: 

1. Whether room air could enter the cage, improving ventilation. 
2. Whether the mice bred in groups or individually (i.e., whether the mice are socially isolated). 
3. Whether the mice had an enriched environment (e.g., toys). 

They tracked two indicators of whether the mice were stressed: the concentration of corticosterone in the mouse’s blood and the mouse’s body weight. Corticosterone is a hormone released when an animal is stressed. Body weight is a useful indicator of stress levels because stressed animals often lose weight. 

On average, the mice in well-ventilated cages had a higher body weight and lower blood corticosterone concentration, suggesting that their stress levels were lower. Mice in enriched environments had higher body weights and lower blood corticosterone concentrations. However, there was no difference in body weight or corticosterone levels between the single and group breeding settings, suggesting this factor didn’t make a big difference in stress levels. In general, the authors argue, the research on whether group breeding improves welfare is mixed, so this result is expected.

This study shows how a laboratory mouse’s living conditions can greatly impact their stress level, and that mice are less stressed if they have well-ventilated cages and an enriched environment. Animal advocates should conduct more research to understand the effects of isolation on laboratory mice, and they should continue to advocate for alternatives to animal models wherever possible.