The guinea pig (Cavia porcellus), also called the cavy or domestic guinea pig, is a species of rodent belonging to the family Caviidae and the genus Cavia. Despite their common name, these animals are not in the pig family, nor are they from Guinea. They originated in the Andes, and earlier studies based on biochemistry and hybridization suggested they are domesticated descendants of a closely related species of cavy such as Cavia aperea, C. fulgida, or C. tschudii and, therefore, do not exist naturally in the wild. Recent studies applying molecular markers, in addition to studying the skull and skeletal morphology of current and mummified animals, revealed that the ancestor is most likely Cavia tschudii.
The domestic guinea pig plays an important role in the folk culture of many Indigenous South American groups, especially as a food source, but also in folk medicine and in community religious ceremonies. Since the 1960s, efforts have been made to increase consumption of the animal outside South America.
In Western societies, the domestic guinea pig has enjoyed widespread popularity as a household pet since its introduction by European traders in the 16th century. Their docile nature and responsiveness to handling and feeding, and the relative ease of caring for them, continue to make guinea pigs a popular pet. Organizations devoted to competitive breeding of guinea pigs have been formed worldwide, and many specialized breeds of guinea pig, with varying coat colors and compositions, are cultivated by breeders.
Biological experimentation on guinea pigs has been carried out since the 17th century. The animals were frequently used as model organisms in the 19th and 20th centuries, resulting in the epithet “guinea pig” for a test subject, but have since been largely replaced by other rodents such as mice and rats. They are still used in research, primarily as models for human medical conditions such as juvenile diabetes, tuberculosis, scurvy, and pregnancy complications.
History: The guinea pig was first domesticated as early as 5000 BC for food by tribes in the Andean region of South America (the present-day southern part of Colombia, Ecuador, Peru, and Bolivia), some thousands of years after the domestication of the South American camelids. Statues dating from circa 500 BC to 500 AD that depict guinea pigs have been unearthed in archaeological digs in Peru and Ecuador. The Moche people of ancient Peru worshipped animals and often depicted the guinea pig in their art. From about 1200 AD to the Spanish conquest in 1532, selective breeding resulted in many varieties of domestic guinea pigs, which form the basis for some of the modern domestic breeds. They continue to be a food source in the region; many households in the Andean highlands raise the animal, which subsists on the family’s vegetable scraps. Folklore traditions involving guinea pigs are numerous; they are exchanged as gifts, used in customary social and religious ceremonies, and frequently referenced in spoken metaphors. They also play a role in traditional healing rituals by folk doctors, or curanderos, who use the animals to diagnose diseases such as jaundice, rheumatism, arthritis, and typhus. They are rubbed against the bodies of the sick, and are seen as a supernatural medium. Black guinea pigs are considered especially useful for diagnoses. The animal also may be cut open and its entrails examined to determine whether the cure was effective. These methods are widely accepted in many parts of the Andes, where Western medicine is either unavailable or distrusted.
Spanish, Dutch, and English traders brought guinea pigs to Europe, where they quickly became popular as exotic pets among the upper classes and royalty, including Queen Elizabeth I. The earliest known written account of the guinea pig dates from 1547, in a description of the animal from Santo Domingo; because cavies are not native to Hispaniola, the animal was earlier believed to have been introduced there by Spanish travelers. However, based on more recent excavations on West Indian islands, the animal must have been introduced by ceramic-making horticulturalists from South America to the Caribbean around 500 BC, and it was present in the Ostionoid period, for example, on Puerto Rico, long before the advent of the Spaniards. The guinea pig was first described in the West in 1554 by the Swiss naturalist Conrad Gessner. Its binomial scientific name was first used by Erxleben in 1777; it is an amalgam of Pallas’ generic designation (1766) and Linnaeus’ specific conferral (1758). The earliest known illustration of a domestic guinea pig is a painting (artist unknown) in the collection of the National Portrait Gallery in London, dated to 1580, which shows a girl in typical Elizabethan dress holding a tortoise-shell guinea pig in her hands; she is flanked by her two brothers, one of whom holds a pet bird. The picture dates from the same period as the oldest recorded guinea pig remains in England, which are a partial cavy skeleton found at Hill Hall (Essex), an Elizabethan manor house, and dated to around 1575.
Name: The scientific name of the common species is Cavia porcellus, with porcellus being Latin for “little pig”. Cavia is New Latin; it is derived from cabiai, the animal’s name in the language of the Galibi tribes once native to French Guiana. Cabiai may be an adaptation of the Portuguese çavia (now savia), which is itself derived from the Tupi word saujá, meaning rat. Guinea pigs are called quwi or jaca in Quechua and cuy or cuyo (plural cuyes, cuyos) in the Spanish of Ecuador, Peru, and Bolivia. Ironically, breeders tend to use the more formal “cavy” to describe the animal, while in scientific and laboratory contexts, it is far more commonly referred to by the more colloquial “guinea pig”.
How the animals came to be called “pigs” is not clear. They are built somewhat like pigs, with large heads relative to their bodies, stout necks, and rounded rumps with no tail of any consequence; some of the sounds they emit are very similar to those made by pigs, and they also spend a large amount of time eating. They can survive for long periods in small quarters, like a ‘pig pen’, and were thus easily transported on ships to Europe.
The origin of “guinea” in “guinea pig” is harder to explain. One proposed explanation is that the animals were brought to Europe by way of Guinea, leading people to think they had originated there. “Guinea” was also frequently used in English to refer generally to any far-off, unknown country, so the name may simply be a colorful reference to the animal’s exotic appeal. Another hypothesis suggests the “guinea” in the name is a corruption of “Guiana”, an area in South America, though the animals are not native to that region. A common misconception is that they were so named because they were sold for the price of a guinea coin; this hypothesis is untenable, because the guinea was first struck in England in 1663, and William Harvey used the term “Ginny-pig” as early as 1653. Others believe “guinea” may be an alteration of the word coney (rabbit); guinea pigs were referred to as “pig coneys” in Edward Topsell’s 1607 treatise on quadrupeds.
Traits and environment: Guinea pigs are large for rodents, weighing between 700 and 1200 g (1.5–2.5 lb), and measuring between 20 and 25 cm (8–10 in) in length. They typically live an average of four to five years, but may live as long as eight years. According to the 2006 Guinness World Records, the longest living guinea pig survived 14 years, 10.5 months.
In the 1990s, a minority scientific opinion emerged proposing that caviomorphs, such as guinea pigs, chinchillas, and degus, are not rodents and should be reclassified as a separate order of mammals (similar to lagomorphs). Subsequent research using wider sampling has restored consensus among mammalian biologists that the current classification of rodents as monophyletic is justified.
Natural habitat: C. porcellus is not found naturally in the wild; it is likely descended from some closely related species of cavies, such as C. aperea, C. fulgida, and C. tschudii, which are still commonly found in various regions of South America. Some species of cavy identified in the 20th century, such as C. anolaimae and C. guianae, may be domestic guinea pigs that have become feral by reintroduction into the wild. Wild cavies are found on grassy plains and occupy an ecological niche similar to that of cattle. They are social, living in the wild in small groups which consist of several females (sows), a male (boar), and the young (which in a break with the preceding porcine nomenclature are called pups). They move together in groups (herds) eating grass or other vegetation, and do not store food. While they do not burrow or build nests, they frequently seek shelter in the burrows of other animals, as well as in crevices and tunnels formed by vegetation. They tend to be most active during dawn and dusk, when it is harder for predators to spot them.
Domesticated guinea pigs thrive in groups of two or more; groups of sows, or groups of one or more sows and a neutered boar are common combinations. Guinea pigs learn to recognize and bond with other individual guinea pigs, and testing of boars shows their neuroendocrine stress response is significantly lowered in the presence of a bonded female when compared to the presence of unfamiliar females. Groups of boars may also get along, provided their cage has enough space, they are introduced at an early age, and no females are present. Domestic guinea pigs have developed a different biological rhythm from their wild counterparts, and have longer periods of activity followed by short periods of sleep in between. Activity is scattered randomly over the day; aside from avoidance of intense light, no regular circadian patterns are apparent.
Domestic guinea pigs generally live in cages, although some owners of large numbers of guinea pigs dedicate entire rooms to their pets. Cages with solid or wire mesh floors are used, although wire mesh floors can cause injury and may be associated with an infection commonly known as bumblefoot (ulcerative pododermatitis). “Cubes and Coroplast” (or C&C) style cages are now a common choice. Cages are often lined with wood shavings or a similar material. Bedding made from red cedar (Eastern or Western) and pine, both softwoods, were commonly used in the past, but these materials are now believed to contain harmful phenols (aromatic hydrocarbons) and oils. Safer beddings made from hardwoods (such as aspen), paper products, and corn cob materials are other alternatives. Guinea pigs tend to be messy within their cages; they often jump into their food bowls or kick bedding and feces into them, and their urine sometimes crystallizes on cage surfaces, making it difficult to remove. After its cage has been cleaned, a guinea pig typically urinates and drags its lower body across the floor of the cage to mark its territory. Male guinea pigs may also mark their territory in this way when they are taken out of their cages.
Guinea pigs do not generally thrive when housed with other species. Housing of guinea pigs with other rodents such as gerbils and hamsters may increase instances of respiratory and other infections, and such rodents may act aggressively toward the guinea pig. Larger animals may regard guinea pigs as prey, though some (such as dogs) can be trained to accept them. Opinion is divided over the cohousing of guinea pigs and domestic rabbits. Some published sources say that guinea pigs and rabbits complement each other well when sharing a cage. However, as lagomorphs, rabbits have different nutritional requirements, so the two species cannot be fed the same food. Rabbits may also harbor diseases (such as respiratory infections from Bordetella and Pasteurella), to which guinea pigs are susceptible. Even the dwarf rabbit is much stronger than the guinea pig and may cause intentional or inadvertent injury.
Guinea pigs can learn complex paths to food, and can accurately remember a learned path for months. Their strongest problem-solving strategy is motion. While guinea pigs can jump small obstacles, they are poor climbers, and are not particularly agile. They startle extremely easily, and either freeze in place for long periods or run for cover with rapid, darting motions when they sense danger. Larger groups of startled guinea pigs “stampede”, running in haphazard directions as a means of confusing predators. When excited, guinea pigs may repeatedly perform little hops in the air (known as “popcorning”), a movement analogous to the ferret’s war dance. They are also exceedingly good swimmers.
Like many rodents, guinea pigs sometimes participate in social grooming, and they regularly self-groom. A milky-white substance is secreted from their eyes and rubbed into the hair during the grooming process. Groups of boars often chew each other’s hair, but this is a method of establishing hierarchy within a group, rather than a social gesture. Dominance is also established through biting (especially of the ears), piloerection, aggressive noises, head thrusts, and leaping attacks. Non-sexual simulated mounting for dominance is also common among same-sex groups.
Guinea pig sight is not as good as that of a human, but they have a wider angle of vision (about 340°) and see in partial color (dichromacy). They have well-developed senses of hearing, smell, and touch. Vocalization is the primary means of communication between members of the species. These are the most common sounds made by the guinea pig:
A “wheek” is a loud noise, the name of which is onomatopoeic, also known as a whistle. An expression of general excitement, it may occur in response to the presence of its owner or to feeding. It is sometimes used to find other guinea pigs if they are running. If a guinea pig is lost, it may wheek for assistance.
A bubbling or purring sound is made when the guinea pig is enjoying itself, such as when being petted or held. It may also make this sound when grooming, crawling around to investigate a new place, or when given food.
A rumbling sound is normally related to dominance within a group, though it can also come as a response being scared or angry. In these cases, the rumble often sounds higher and the body vibrates shortly. While courting, a male usually purrs deeply, swaying and circling the female in a behavior called “rumblestrutting”. A low rumble while walking away reluctantly shows passive resistance. Chutting and whining are sounds made in pursuit situations, by the pursuer and pursuee, respectively.
A chattering sound is made by rapidly gnashing the teeth, and is generally a sign of warning. Guinea pigs tend to raise their heads when making this sound.
Squealing or shrieking is a high-pitched sound of discontent, in response to pain or danger.
Chirping, a less-common sound, likened to bird song, seems to be related to stress, or when a baby guinea pig wants to be fed. Very rarely, the chirping will last for several minutes.
The guinea pig is able to breed year-round, with birth peaks usually coming in the spring; as many as five litters can be produced per year. The gestation period lasts from 59–72 days, with an average of 63–68 days. Because of the long gestation period and the large size of the pups, pregnant females may become large and eggplant-shaped, although the change in size and shape varies. Unlike the offspring of most other rodents, which are altricial at birth, newborn pups are well-developed with hair, teeth, claws, and partial eyesight; they are immediately mobile, and begin eating solid food immediately, though they continue to suckle. Litters yield one to six pups, with an average of three; the largest recorded litter size is 17.
In smaller litters, difficulties may occur during labour due to over-sized pups. Large litters result in higher incidences of stillbirth, but because the pups are delivered at an advanced stage of development, lack of access to the mother’s milk has little effect on the mortality rate of newborns. Cohabitating females assist in mothering duties if lactating.
Guinea pigs also practice alloparental care, in which a female may adopt the pup or pups of another. This might take place if the original parents die or are for some reason separated from them. This behavior is common, and is seen in many other animal species such as the elephant.
Male and female guinea pigs do not differ in external appearance apart from general size. The position of the anus is very close to the genitals in both sexes. Female genitals are distinguished by a Y-shaped configuration formed from a vulvar flap, while the male genitals may look similar, with the penis and anus forming a like shape, the penis will protrude if pressure is applied to the surrounding hair. The male’s testes may also be visible externally from scrotal swelling.
Males reach sexual maturity at 3–5 weeks; females can be fertile as early as four weeks and can carry litters before they are adults. Females that have never given birth may develop irreversible fusing of the pubic symphysis, a joint in the pelvis, due to calcification which may occur between six and 10 months of age. If they become pregnant after this has happened, the birth canal will not widen sufficiently; this may lead to dystocia and death as they attempt to give birth. Calcification of the female’s pubic symphysis (if not bred) is a common myth. The reason for potential calcification is a metabolic disease, like ochronosis. A healthy, normal female guinea pig’s pubic symphysis does not calcify. Females can become pregnant 6–48 hours after giving birth, but it is not healthy for a female to be thus constantly pregnant.
Toxemia of pregnancy is common and kills many pregnant females. Signs of toxemia include anorexia, lack of energy, excessive salivation, a sweet or fruity breath odor due to ketones, and seizures in advanced cases. Pregnancy toxemia appears to be most common in hot climates. Other serious complications of pregnancy can include a prolapsed uterus, hypocalcaemia, and mastitis.