Cages for the rat, like those for the mouse, are usually made of non-toxic plastic with a solid bottom and a metal grid cover (steel or another painted metal can be used, provided that the paint is non-toxic) (Fig. 1). There are no precise rules concerning rat cages and their dimensions, but based on personal experience, the author suggests a floor area of at least 40 cm x 50 cm in order to accommodate one or two animals, but larger areas are well accepted.
Since the rat is a fairly good climber, the cage should be high (at least 75 cm) with several levels. The rat is a very intelligent, inquisitive animal and a stimulating environment is essential for the mental health of this large rodent. Pipes, ladders, hideaways or boxes, rubber or plastic balls and any other specifically designed games will, therefore, be very useful. However, the rat is also satisfied with simple materials such as cardboard, paper (especially absorbent kitchen roll) and wood which it will use to file its teeth or shred into thousands of pieces to fill and insulate its hideaway.
It is very important that the rat is left free in a room for at least a few hours each day in order that it can explore the environment and perform functionally useful exercise. However, care must be taken with regards to anything that can be gnawed (furniture and electrical wires): the rat shows a marked “tropism” for armchairs and settees, which it will dig into deeply. The room in which the animal is left free must, therefore, be “rat-proof”, otherwise the pet must be watched all the time.
Rats can be reared in colonies, even though it is sometimes necessary to isolate aggressive subjects and house them individually. As for mice, colonies of rats should not be too numerous because overcrowding encourages the onset of aggressive behaviour. Male rats are less aggressive than mice and, therefore, if they have been reared together they can remain in the same cage as adults. However, if several male rats are housed together or in the company of female rats, castration should be considered.
The bottom of the cage is usually a solid floor covered by bedding because this is more comfortable than a grid as a floor. Sawdust or, better still, fine wood shavings can be used for the bedding, provided that they are microbiologically pure and non-toxic (for example, pine and cedar are very harmful), but corncobs and wood pellets are also widely used.
Scraps of paper, wool, cotton or cotton wool can be used as material for the nest, although some females may choose to give birth anyway in burrows dug in the bedding.
It is very important that the microclimate is suitable for the animal and that swings in temperature and humidity are avoided because the rat is susceptible to respiratory tract disorders, which are favoured by these factors. The recommended temperature is about 20°C (even if rats adapt well to a very broad range of temperatures), while the relative humidity should be from 60-70% and the photoperiod consist of 10-12 hours of light.