Keeping guinea pigs
Guinea pigs originated in South America but were probably introduced into Europe soon after the first Spanish explorers returned from that continent in the 1500s. Even though they came from a tropical area these rodents proved to be hardy and adapted to temperate climates such as that of Britain. They became favourite pets in the early part of this century and are also bred as show animals with a wide variety of coat colours and fur types. Feeding your guinea pig is covered in a separate leaflet - here we cover housing and breeding.
This is not particularly difficult and a large variety of hutches and cages have been used. Guinea pigs can be kept outside in the summer and a good draught-free but well ventilated mobile run on the grass is very acceptable as long as there is also a dry covered area. Pens should be at least 30cm high to avoid escapes and should be covered with mesh to keep cats out. Indoor cages in the winter should allow at least 0.2 square metres of floor space per guinea pig. Since they are social animals guinea pigs can be kept in small to medium groups, but clearly mating will increase the number of animals so single sex groups are advisable. Temperatures between 12 and 20°C are ideal. Anything over 27°C will lead to heat-stroke, especially in animals that are overweight or pregnant.
Guinea pigs are one of a group of rodents called the hystricomorphs with an unusual reproductive physiology and breeding strategy. Chinchillas are another member of this group and the others, such as the plains vichaca are not kept in captivity so will not be discussed here.
Guinea pigs mature at around 3 months but should not be used for breeding for another three months. After about eight months of age the female guinea pig's pelvic bones become more tightly fused and if she has not had a litter by that time, producing young can be more of a problem. You might ask why that is a problem since animals of most species can delay giving birth until they are older. The difference with the guinea pig is that she gives birth not to a large litter of tiny immature young (as the rat or mouse does), but to between two and four fully developed well furred offspring. The average gestation period is 63 days. These large babies have a hard time getting through the pelvic canal unless the mother's pelvic bones are relatively immature and malleable. These large offspring predispose the mother to pregnancy toxaemia. This is a metabolic disorder resulting in low blood calcium and high blood pressure. It manifests as loss of appetite in the early stages, deteriorating to muscle twitching and coma. Prompt veterinary attention can save animals but the problem can be reduced to a minimum by providing plenty of water and green foods during pregnancy, as throughout life.
There is a relatively high incidence of dead babies and if the gestation should continue over 70 days, it is likely that the litter will be lost. The guinea pig, along with other hystricomorph rodents, starts off with a much larger set of foetuses in her uterus but many of them die before birth, some early on but some later in gestation, or even at birth. The reason is unclear but it may be a mechanism of producing the maximum number of babies for a limited and varying food supply.
As with many rodents the female guinea pig will be able to mate within a few hours of giving birth. She should not be allowed to, however, since it is much better that she has time to replenish her metabolic reserves before becoming pregnant again. If your guinea pig has a large litter of over three or four piglets it is worth fostering some off onto another sow, since guinea pigs have only two nipples to suckle their offspring.
Feeding your guinea pig
Guinea pigs are herbivores rather like rabbits, although the physiology and function of their gastrointestinal system is less well understood than that of the rabbit which has been well investigated. The critical area of dietary science in guinea pigs of which you should be aware is their requirement for vitamin C, covered further below. Apart from that, the key to a healthy diet in a guinea pig is variety. Imagine what the guinea pig has to eat in its native environment of the South American forests: a bit of everything from fruits through greens and grasses to root vegetables. We often mistakenly feed a dry guinea pig mix with few fresh vegetables and expect that to satisfy the animal's requirements. It does not.
For every animal there is a set of essential nutrients and another set of non-essential nutrients. Animals need a regular dietary supply of essential ingredients, while they can produce their own supply of the non-essential nutrients. These essential elements differ between species so that, for instance, the cat and ferret require a regular supply of the amino acid taurine while other mammals such as ourselves can produce taurine by metabolising other amino acids. In the guinea pig and man one key essential nutrient is vitamin C. The vast majority of other animals can produce their own vitamin C from their intestinal bacterial flora but this metabolic pathway in guinea pigs and humans has been lost. (This is why eighteenth century sailors developed scurvy when not able to eat fresh fruit). Vitamin C is vital in the normal development and maintenance of skin and mucosal surfaces such as gums. It is also important in the healing of wounds to these structures. As well as predisposing to skin problems, a lack of vitamin C seems to make the body more prone to other diseases, infections and poor condition. A guinea pig which is reluctant to walk, has swollen feet or haemorrhages and ulcers on its gums or elsewhere is likely to be deficient in vitamin C.
There is no reason why a guinea pig should be deficient in this nutrient, since it is available from fresh fruit and green vegetables. But it is a relatively unstable compound. If you are giving only a dry mix with old hay, most of the vitamin C will have decomposed by oxidation. If your guinea pig develops a deficiency, it is much better to give a crushed tablet by mouth rather than in drinking water, since the vitamin breaks down in water and loses its potency. To ensure vitamin C in the diet feed fresh grass, broccoli and red peppers which have a very high level of the vitamin.
What else to feed?
Given that guinea pigs are adapted to a diet of fibrous vegetable matter, good quality grass or hay is absolutely essential and should make up the bulk of the diet. A few high vitamin C content fresh vegetables should be given daily. A diet of this type will keep your guinea pig happy and healthy.