How to Control Variability in Testosterone Levels in Mice

Separate any male mice housed in the same cage in their own cages. Typically, mice are housed in groups of four or five, but aggressive males will dominate submissive males and the stress will cause testosterone levels to fluctuate. Placing mice in their own homes reduces most variability in testosterone levels.

House your male mice in a separate room from the female mice. The presence of female mice, especially when the females enter their fertile time of the estrus cycle, will increase the testosterone levels in the male mice.

Handle all female mice in one session. Wash your hands or change gloves before handling the male mice. For example, clean all the females' cages, wash your hands and then change all the males' cages. This keeps the scent of the females away from the males and reduces the chance of a testosterone level increase from the scent.

Wash your hands or change gloves after handling any one male mouse for a long period of time if you will be handling another male mouse afterward. This keeps the scent of the first male from raising testosterone levels in the second male. An example of this type of handling is during surgery or when setting a mouse up for an experiment.

Wash anything in which a male mouse has come into contact before letting another male mouse come into contact with the item. Better yet, keep separate items for each male mouse such as water bottles and food dishes. If male mice must use the same experimental chamber after one another, spray the chamber down with dilute alcohol and wipe it down well.

Neuter your male mice. This is a last resort effort and should only be employed if mice are extremely aggressive as the alteration may change the mouse's behavior enough to change the results of your experiment. This should also only be done if you will not need to study the mouse's testosterone levels later in your experiment. For consistency, if you neuter one male mouse in your experiment, you should neuter all the male mice for the entire experiment.