The cage in which a guinea pig is kept must be bite-proof and escape-proof. Guinea pigs do not climb and so it is not necessary that the top of the cage is closed, provided that the walls are at least 25 cm high. If the cage is left open it is essential that dogs and cats do not have access to it.
The recommended materials are steel, plastic and Plexiglas, while wood is not suitable for reasons of hygiene. There should be no sharp edges or pointed tips which could cause wounds. The recommended size of a cage is about 600 cm2 for an adult and about 1000 cm2 for a female with a litter of young. Larger cages can be built by hand or several cages can be connected to each other in order to allow the animals to take more exercise.
The bottom of the cage should preferably be solid because guinea pigs have relatively small paws in relation to the weight they must support and a grid could favour the development of pododermatitis or cause fractures. The lower part of the cage should have relatively high side walls in order that material in the bottom does not fall out continuously. The height of the cage is not important because guinea pigs do not jump or climb up bars; a height of at least 20 cm should be sufficient. For the same reason, it is not essential to cover the top of cage as long as there are no dogs, cats, ferrets or small children in the house.
The bottom of the cage should be covered with soft, absorbent material that is harmless to the animal; this material should not be powdery, otherwise it could be inhaled. Sawdust and wood shavings are not a good choice because they can pack the genital area, creating serious problems. Course straw can cause wounds, in particular to the eyes. Suitable materials include good quality hay, pellets of corncob or recycled paper (which can be found in pet shops) and pieces of paper. Cleaning the cage can be greatly facilitated by placing sheets of newspaper on the bottom of the cage and covering this with the litter; the newspaper and the litter can then be removed together. The litter must be deep and always very clean in order to safeguard the animal’s paws.
An indispensible cage accessory is a box. Guinea pigs are very timid animals and when they do not feel safe they run to hide themselves in a sheltered place. A box enables the guinea pig to take shelter whenever it feels the need, with indubitable advantages from a psychological point of view. The box also constitutes the essential nest in which the guinea pig can sleep during the night. The box may be of wood or cardboard and should be replaced when it becomes dirty or too damaged by gnawing. It should not have toxic materials (paint) or parts that would be dangerous if ingested (pieces of adhesive tape, for example) or could wound the guinea pig (nails, metal staples, splinters).
Other accessories are racks to contain hay and vegetables, recipients for fodder (preferably ceramic because they are less easily overturned) and water bottles. Guinea pigs tend to enter their food bowls to defecate so these recipients should be fairly small in order to prevent the animals from entering them. The water bottle, which must have a spout, should be hung on the wall of the cage and the water within it must always be clean. It is important to check that the water delivery system works correctly: guinea pigs like blowing into the spout, clogging it up with food particles and blocking the free release of the water.
The cage must be placed in a peaceful place without bothersome noises (rowdiness, stereos, radios, television) or confusion and must be inaccessible to dogs, cats and ferrets. Guinea pigs are easily frightened by sudden noises and the presence of potential predators.
The ambient temperature should be kept between 18 and 26°C; the ideal temperature is 21°C. A healthy guinea pig with a box hide available can withstand lower temperatures, but is very sensitive to draughts and cold. High temperatures are also poorly tolerated, particular when the humidity is high. Guinea pigs do not sweat and have a very compact body which does not easily dissipate heat; high temperatures (even only above 27°C) can cause their death. The relative humidity of the environment should be kept between 30% and 70%. Care must be taken to locate the cage in the coolest part of the house during the hot season. The cage must not be exposed to direct sunlight (for example, by being in front of a window or on a terrace), because excessive heat will kill a guinea pig in a very short time and, confined in a cage, the animal cannot go anywhere to find a cooler place. For the same reasons the cage should not be placed next to an air conditioner or a radiator.
It is difficult to train guinea pigs to use a tray and they deposit faeces and urine all over the place; furthermore, they tend to gnaw anything they come across. For this reason it is better that they are not left free to roam around the house unless they are kept under direct surveillance and someone is prepared to clean up after them. In any case, the guinea pig should be prevented from approaching electrical wires, toxic substances and poisonous plants and must have an escape route.
Guinea pigs suffer greatly from loneliness and should not be kept in captivity alone. A male can be kept together with one or more females (up to five) to constitute a “harem”, in the case that breeding is desired. Two adult males must never be kept together in the presence of females, because the males are very protective of their territory and combative and could cause each other serious harm. On the other hand, two or three males can live together harmoniously provided that a female is never introduced. Sterilisation of the male, if performed when the animal is still young, eliminates the problem of aggressiveness between males and also, obviously, that of unwanted offspring.