The mouse is a very active and inquisitive animal and, therefore, needs appropriate housing. An ordinary cage for rodents can be used for this purpose: the cage may have plastic walls (Fig. 1) or a metal grid, provided that it prevents the animal from escaping (Figs. 2 and 3). As far as concerns enrichment of the environment, any whim can be satisfied, from play houses, to ladders, wheels, tubes and toys of any type. Mice adore anything that they can gnaw and chew into a thousand pieces (for example, paper and cardboard). The size of the cage should be different depending on the number of animals but precise indications on this issue are not available; we can, therefore, only report that the Italian Legislative Decree n. 116 of January 27, 1992, which regulates the well-being of laboratory animals, states that the minimum advised floor area of a cage is 200 cm2 for a pair of adults or for a mother with her litter until weaning, while the height should be at least 12 cm to allow the animal an erect posture. In the case of animals housed in groups (more than two subjects), an additional area of at least 80 cm2/animal is recommended. Cages with more than one level are, in any case, much appreciated.
Widely sold substrates for rodents can be used for the litter, the first and foremost being wood shavings. The litter must be abundant (1 cm) and changed at a variable frequency such that it does not produce an unpleasant smell and is always dry and clean. It is recommended that, on average, the cage should be disinfected once a week, taking care to dry it thoroughly and completely before returning the animal. The litter must in any case respect the general rules of being microbiologically pure, non-toxic and dust-free; thus discarded sawdust and derivatives of pine and cedar should be avoided.
A colony of mice should not comprise more than 30 animals otherwise problems of hierarchy could develop with a consequent increase in stress; furthermore, overcrowding could promote the onset of aggressive behaviour. Mice reared alone are more hostile towards their conspecifics than are mice accustomed to life in a society.
As far as possible the animals should be provided an appropriate microclimate without fluctuations in environmental conditions, maintaining the temperature between 20-24°C (although the mouse is extremely adaptable to any condition and supports even considerable climatic changes well), a relative humidity around 50-60% and a photoperiod as similar as possible to the natural one.
A small box entirely within the cage can be used as a nest, but is not indispensable since the gravid female will make a comfortable “nursery” by digging a small burrow in the litter or by using other material available (Figs. 4 and 5).
