The importance of ventilation is that decomposing droppings and urine give off ammonia. This irritates the respiratory tract, making rats vulnerable to respiratory problems (breathing difficulties). Litter on the cage floor absorbs moisture from droppings, which slows or halts the decomposition process, but some ammonia release is inevitable, even with the best litter. Good ventilation allows ammonia to dissipate in the surrounding air, thus reducing the amount that rats are exposed to in the cage. Ventilation is therefore a very important element in keeping rats healthy, and should be given particular attention whenever a rat suffers from respiratory illness.
Wire cages are by far the best housing for rats. In addition to providing good ventilation they are a ready-made rat climbing-frame, and they allow you to interact with your rats — you can feed and stroke them through the bars. Rats have keen senses of hearing and of smell; a cage provides extra stimulation as your rats can pick up new smells and sounds which they find interesting. Don’t worry about cages being draughty – all that is needed is a warm, sheltered nestbox for a sleeping place.
A cage can be easily converted into a rat adventure playground with a little imaginative use of ropes, ladders, tree branches, shelves, hammocks, and flowerpots attached to the sides. In addition to a minimum of two square feet of floor-space, you should try to get a nice tall cage for your rats: they love to climb, and you can maximise the available space by making shelves. The simplest shelves are melamine boards which can slide between the bars of the cage; they are convenient to remove and can be wiped down. Fer-Plast and other companies make excellent, reasonably priced parrot or cockatiel cages (such as the Fer-Plast Sonia 24″ long x 15″ wide x 25″ high or the Immac Gabbie Dora ) that are suitable for rats. It is worth shopping around, as prices can vary by as much as 100%; animal exhibitions are a great place to get large cages at wholesale prices. Used ads papers (such as LOOT in London) and classified ads are also good places to find cheap cages; make sure that you disinfect and rinse any second-hand cage thoroughly. A hamster cage, no matter how ‘large’, is not suitable for adult rats: even the three-storey ‘hamster-palaces’ do not have enough floor space or climbing opportunities.