Guinea Pig Facts - An Overview

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I General facts
- Life expectancy
- What are males, females and babies called?
- What is the group name for guinea pigs?

II Origin and history
- Guinea pig relatives and wild guinea pig species
- Domestic guinea pigs
- How have guinea pigs got their name?
- Famous guinea pig owners

III Important reproductive and biological facts
- Sexual maturity and reproductive cycle
- Body facts

IV Society and life cycle
- How does guinea pig society work?
- A guinea pig life cycle

Part I: General Guinea Pig Facts

Life expectancy
Average life expectancy of a healthy pet guinea pig: 5-6 years (4-7 years).
The current indiscriminate mass breeding of guinea pigs seems sadly to have an effect on life expectancy!

Longest living documented guinea pig: Sweetie from Australia died aged 17 years in 2014.
Sweetie, the World's Oldest Guinea Pig | Facebook
The previous and still listed Guiness book record holder, Snowball from England, lived to 14 years and 10 months and passed away in 1979.

What are males, females, babies called?
Male guinea pigs are boars, females sows and babies are called pups.

What is the correct mass noun for guinea pigs?
The official mass noun for guinea pigs living together is a 'group of guinea pigs'.
Somebody must have been really unimpressed or have suffered from burnout when naming them!

Guinea pigs ARE group animals and should not be kept as singles.
They are not wired to be on their own and it is very cruel for them to not have any interaction with their own kind!


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Part II: Origin and history

Where do guinea pigs come from?
Guinea pigs or cavies are rodents that have evolved in the grassland and wetlands as well as the lower Andes mountains of South America (Brazil, Uruguay, Peru and Argentina), where they roam around established territories in groups.
They are prey animals. They do not burrow or climb, but can walk quite long distances twice daily between their base in a safe abandoned burrow and their current grazing patch. They move in single file lines along established paths.

Which species are their closest relatives of guinea pigs?
Their closest relatives are the capybaras, which live semi-aquatic lives in swamps, savannah type grasslands or densely forested areas in or near larger, seasonally flooded bodies of water. Capybaras are much larger than guinea pigs, with longer legs due to their spending a lot of time in the water and because of their size, also a longer pregnancy; the longest of all rodents. They give birth on dry land, with mother and babies joining their mates just a few hours later. Capybaras also live in South and Central America.

capybara cred. Cincinnati Zoo.jpg
(Capybara, picture credited to Cincinnati Zoo)

Recently, 100,000 year old fossilised footprints of a close relative of the modern capybara have been found in the Miramar area of Buenos Aires in Argentina, as this article from June 2018 shows.
They identify the fossil footprints of a capybara that lived 100,000 years ago in Miramar.
capybara fossilised footprints Miramar Argentina 2018.jpg

Wild guinea pig species
Guinea pigs have been in existence since the middle pleistocene (ca. 700,000-125,000 years).

There are several wild species of guinea pig in existence today.
Here are the most important:
- cavia magna (greater guinea pig), living in wetlands and small coastal strip in Southeast Brazil and Uruguay
- cavia intermedia (Moleques do Sul guinea pig), a very small population of guinea pigs on tiny islands (4 ha) in Santa Catarina state in Southeast Brazil that is at acute risk of extinction. They are though to have split from cavia magna about 8000 years ago when rising sea levels split the islands from the main continent.

- cavia fulgida (shiny guinea pig), a little known species living in marshlands in Central Brazil, but also in protected areas in Southeast Brazil.

- cavia aperea (Brazilian guinea pig), the widest spread wild guinea pig species found in scrub grasslands and savannahs in all South American countries except Chile, but - as their common name suggests, the majority live in Brazil.
- cavia tschudii, (montane guinea pig), a subspecies of cavia aperea that lives mostly along rivers (including boggy areas) or dense grasslands in a variety of habitats in the Andes from Peru, Bolivia, Chile and Argentina and can be found from sea level to 5000 m altitude (typically between 2000-3800 m).

Cavia aperea Gustavo Fernando Duran.jpg
Cavia aperea, the wild ancestor species of the domestic guinea pigs
(picture credited to Gustavo Fernando Duran)


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Domestic guinea pigs
Cavia porcellus are domesticated guinea pigs
(which we mainly know as our pet guinea pigs) that are descended from cavia aperea via cavia tschudii, as recent analysis of their genome has found.

The DNA analysis also clearly shows that Cavia Porcellus (our guinea pigs) as a species have not evolved naturally. They have been bred by humans and do not naturally interbreed with their wild ancestors.

How do domestic guinea pigs compare with wild species?
Wild Brazilian guinea pigs live in small family groups of one male with 1-2 females and their offspring, often in a number of these core groups fairly close together with adjoining territories. They do not burrow, but use tunnels and pathways in dense undergrow. Males are keen to scent mark the guinea pigs in their groups and can be aggressive to other males. But they will feed in larger groups as this gives them more safety. An average group territory is around 800 square metres.
Domesticated guinea pigs tolerate living much closer together in larger groups with tiny territories as they do not have the same feeding pressures and the space to spread. You will however find that they form little sub-groups within a larger group that tend to hang out and sleep together. They will still travel twice daily for up to a mile to their current feeding ground as a group as a recent scientific experiment has shown.

Wild guinea pigs are generally a little smaller than domestic ones (ca. 500-800g); they breed up to 4 times a year from April to September when there is enough fresh food around. They have generally around 2 babies at a time, but can have litters ranging between 1-5 pups. Wild guinea pigs can live up to 8 years (10 years in captivity), but the average life span is 3 years.

Compared to their wild cousins, domesticated guinea pigs have a brain that is 13% smaller since they do not have to memorise the details of a large territory, but despite having less data storage space they are much better at problem solving when it comes to working out how to get at food, as a recent research trial has found.

Domestic guinea pigs are not equipped to fend for themselves when they are let 'free' or are dumped in parks, by the roadside or in the country. In fact, they will likely be killed by cats, dogs or wildlife or fall ill and die a miserable death. They do not survive a frosty winter in the UK or the US!

Dumping is a coward's way of killing a pet. If you really cannot keep your guinea pigs any longer, please google and contact your closest rescue that will take in cavies to give your guinea pigs a chance at the happy life that they deserve!

When have guinea pigs become domesticated?
Our guinea pigs have been bred as domestic South American farm animals for 3000-6000 years
Guinea pigs have provided a much needed, easily available source of protein in a notoriously variable climate in the centuries before the introduction of other domestic Eurasian animals like chickens, pigs, sheep and goats in the wake of the discovery of the Americas ca. 500 years ago.

This is also reflected in their cultural role, which is documented in Andean art over nearly 2000 years where guinea pig meat was a firm part in the large communal and religious feasts that cemented social cohesion within societies and also between different societies. Guinea pigs are still a popular meat in Andean countries, especially Peru.

Moche art guinea pig vessel from Larco museum, Lima in Peru, dating 200 AD (ca. 1800 years old)
View attachment 91060

When have guinea pigs reached Europe as pets?
Guinea pigs have reached Europe in the 16th century in the wake of the Spanish conquest of South America
, that is nearly 500 years ago. The earliest picture of a guinea pig has recently come to light in a Tudor period children's portrait.
During the first few centuries after their introduction, guinea pigs were pretty rare and very much a rich people's curiosity pet.
View attachment 91062
(National Portrait Gallery)

Today guinea pigs are still a popular meat animal in countries like Peru. Recently, domestic guinea pigs have been outcrossed with wild guinea pigs to produce a much larger and meatier guinea pig specifically for the South American meat production. Due to the wild genes, so-called Cuys are often much more skittish and very difficult to handle unless you are a very experienced guinea pig keeper. Sadly, they have somehow got into the supply chain of Californian pet shops and are currently causing havoc in unsuspecting US families.

How have guinea pigs got their name?
The species name of our domestic guinea pigs is cavia aperea, formerly cavia porcellus. Cavia, the latinised species name, comes from “cuy”, whereas the old name porcellus means “little pig” in Latin, which they have got because of the sounds they make.
This has then given rise to "cavy" as the more common expression for guinea pigs in North America.
The species has been recently renamed in the wake of determining the genetic wild ancestor species (there are three wild species of guinea pigs in South America) from which the domesticated species has been bred out from.

Nobody really knows how guinea pigs have got their English name; but cavies very obviously do not come from the historic Guinea area in Africa (roughly the coast around Ghana - which may have provided the name 'Guinea' - reaching down towards the Kongo), even though one theory explains the name from the trade winds supported ship routes from South America using gold rich Guinea as stopover on the way home.
They have never cost a guinea (which is a coin that used to be made from gold mined in Guinea).
You can however find all kinds of theories on how to make a connection between Guinea and these South American curiosity pets; most of them not exactly satisfying!

By far the best - if not well known - explanation that I have come across so far is that “guinea” is simply a language transfer of the unfamiliar “cuy/cuye/cuya” (the South American name for guinea pigs, originating from their “kooee" or "kwee" sounds) to a similar sounding familiar English word.
This is a well-known language mechanism for foreign or difficult/obscure technical words that spill over into common speak. Rotten Row in Hyde Park in London for instance started out as Route du Roi, "the King's Road", as a striking example of this. A modern example for the same still active language process is the increasing spelling of 'tenterhooks' as 'tenderhooks' with the old naval meaning having become obsolete in the modern age.

Here is a list of how guinea pigs are called in other languages: How To Say Guinea Pig In Different Languages

Famous guinea pig owners

US president Theodore Roosevelt grew up with several guinea pigs and so did his children.
Here he is with his family and all their guinea pigs. He is the boy on the right.
The guinea pigs were called Admiral Dewey, Bishop Doane, Dr Johnson, Father O'Grady and Fighting Bob Evans!
View attachment 91061

President Roosevelt's children with a guinea pig
Roosevelt's son Kermit with guinea pig and sisters.jpg

Princess Diana had a much loved guinea pig called Peanut as a teenager.
Diana with Peanut 1970, digitally coloured (image Camera Press) .jpg


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Part III: Reproductive and biological facts

Sexual maturity and reproductive cycle
Males: between 3-5 weeks (Please separate baby boars at 3 weeks old/250g of weight!)
Females: between 4-6 weeks
Earliest documented sibling pregnancy: 24 days

Sows come into season again within hours of giving birth. Their oestrous cycle (how often they come into season) is 15-17 days.

A pregnancy lasts between 58-73 days. Guinea pigs can have up to 10 babies in one litter (the largest fully surviving litter is 8 pups), but normal are 1-6 pups.
Guinea pigs have the longest pregnancy and smallest number of babies of all rodents. But a long pregnancy and big babies mean that about 20-25% of pregnancies with the death of pups and/or their mothers because of their large size and the high risk this poses.

Newborn pups are precocious, i.e. born fully furred, with their eyes open, their teeth fully developed, able to follow their mother and to nibble on solid foods straight away although they depend on their mother's milk for 3-4 weeks when they are weaned by their mothers and become sexually active straight away.
They learn what is safe to eat and how to drink from their elders and continue to rely on them for guidance and socialisation until they reach the teenage months and they become parents themselves.
If babies are not properly sexed and any boars separated from sows at 3 weeks of age, they can multiply and get our of hand very quickly!

Boar testicles start descending coming up to around 4 months of age, which signals the start of the teenage, which is characterised by big testosterone spikes (ca. 4-14 months). They are usually fully descended by 6 months which coincides with the time testosterone production is at a lifetime high. Unlike in humans, the descent of the testicles doesn't signal sexual maturity; it happens well after the fact!

End of reproductive age for males and females: no end until death. There is no menopause for guinea pigs; but the older they are, the higher the risk of death for the sow and any pups, especially first time mums!

Body facts

Guinea pigs have much finer hearing than humans; they can hear higher sounds than humans, which is not surprising, considering that they have evolved in dense grasslands where hearing is much more vital than sight!

Accordingly, guinea pigs can see very clearly in colour on short distances (reddish shades are somewhat differently perceived compared to humans), but over larger distances they only react to sudden movements. This is important when trying to avoid spooking them.
Like most prey animals, their eyes cover a wide area to the sides and above, but they cannot see in front of their nose. This area is covered by a strong sense of smell and by their whiskers, which are an additional sense.
When guinea pigs eat, they find their morsels by smell as they cannot see what they are picking up. This is also the reason why they can mistakenly bite into a finger of yours that smells of fresh veg!
Since they are prey animals, guinea pigs will sleep with their eyes fully closed only if they are absolutely exhausted or feeling totally safe where they are. Mostly you can spot a sleeping piggy by the far-away look in its eyes.

Like with all rodents, their teeth grow constantly and have to be worn down through eating in order to avoid them overgrowing. In fact, guinea pigs seem to have the fastest growing teeth of all rodents!
In a healthy dental system, the front teeth are self-sharpening and don't need any attention. The molars and premolars at the back are ground down through the silica in grass and hay; this is why hay should make up to 80% of the daily food intake.
Their guts have also evolved to cope specifically with their natural diet; too rich a diet of vegetables and fruit leads to fermentation in the gut, and long term health is compromised!

Digestive system
Guinea pigs have to digest everything they eat twice in order to break down the tough fibrous hay/grass that is what they should mostly eat - over 80% of their daily food intake with only a little veg and just a tablespoon of pellets each day. A little fruit should only be on the menu twice a week. The more hay a guinea pig eats, the healthier it will be and the longer it has a chance at living.

Two runs through the gut means that guinea pigs have two sorts of poos which they produce at different times. The ones they eat for redigestion to get as much nutrition out during the second run through their large gut are called caecotrophs.
Because guinea pigs have evolved to live off nutrionally rich, but difficult to extract food, they need eat a lot for their size; they also make a lot of poos - which is the sign of a health piggy!

Unlike rabbits, guinea pigs can't make their own vitamin C and need to have have vitamin C in their diet.

Guinea pigs rely on a steady supply of food; they cannot fast for more than a day at the very most or they will die. A guinea pig that is not eating much or nothing at all needs to be syringe fed with fibrous recovery food and water (only water will not keep it going). It needs to see a vet promptly or its guts will start to slow down after a day and then shut down; the guinea pig will die when that happens.

Vomiting reflex
Guinea pigs don't have a vomit reflex (typical for all rodents) - what has gone down has to come out at the other end! To avoid poisoning, they have double the amount of taste buds than humans and a multiple of that of cats. They learn what is safe to eat from the elders in their group; that is why you can often see babies snatching food from their mouths. They also learn where and how to drink from by mimicking other piggies.

Guinea pigs have four digits on their front feet and three on their back feet. They use the front feet to carry the main weight of the body and the back feet as springs when they run very fast.

Nipples and sexing
Males and females have both got 2 nipples that look the same. Young babies often look very similar when they are born and are often mis-sexed by shop personnel or breeders which can result in unplanned pregnancies.
Here is how you can sex guinea pigs safely: Sexing Guide
How you can learn to spot what is normal and what not in a guinea pig body: Guinea pig body quirks

Heart rate and breathing
Guinea pigs have a much faster heart rate than we humans.
They cannot breathe through their mouths, which is why every little obstruction in their narrow airways is very audible.

Regulating the body temperature
Guinea pig regulate their body temperature via the blood flow through their ears. They do not sweat or pant. Any dampness in the fur comes from condensation in a confined, not well aired space. Guinea pigs do not need a lot more fluid in hot weather, but they need to be kept cool and have access to cool, fresh water at all times!

That is not very efficient when guinea pigs are exposed to sudden swings of temperature (day/night or taking a guinea pig outside in weather extremes). They also struggle with heat over 25 C or frosty conditions because they are used to living in more stable conditions. They can cope with somewhat warmer stable conditions of they were born in these, but still struggle with the extremes and are even more vulnerable to sudden cold spells and night temperatures below 10 C.
Guinea pigs can quickly die from heat stroke when left outdoors in hutches or runs or are left in sunny indoors rooms with open windows and a fan going in hot weather.
They can also die from cold in winter in uninsulated and unprotected outdoors hutches.

Bladder and urine
Guinea pigs have a very alkaline urine, which means that they are prone to infections of the urinary tract as well as bladder stones because this makes it easier for bacteria to thrive and less effective when dealing with calcium.
Please make sure that you do filter any water (especially in high water areas), stay off high calcium veg and and check the calcium content in your pellets. Opt for for low calcium, grain-free pellets whenever you can.

Metabolism and dangerous medications
Guinea pigs have a very fast metabolism in order to cope with all the food they have to eat efficiently. They also absorb medications much faster than cats or dogs and need much higher dosages compared to their body weight. Most medication should be given twice daily to maintain a steady level, especially painkillers.

Did you know that penicillin-based antibiotics kill guinea pigs and that steroids are bad news for them?
Always make sure to ask beforehand what your vet, especially an emergency vet, is injecting!
Guinea Lynx :: Dangerous Medications
The Problems With Steroids And Why They Shouldn't Be Used.


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Part IV: Guinea pig society and life cycle

How does guinea pig society work?
The territories of wild guinea pig groups are usually about as big as necessary to keep the group fed; in the thick undergrowth, the roaming animals stay in touch by voice. Even now you can see pet piggies moving nose by tail in a clucking single file, led by a senior group member.
Guinea pigs make paths through the grasslands and can memorise all the ways in their territory, so they do not get lost. Domestic guinea pigs have lost this ability since they have very small territories.

Guinea pigs don’t burrow, climb or build sets, but they happily use any abandoned deep burrows from other animals, tunnels or thick undergrow that have a stable temperature at their deeper reaches and will trek quite a distance in order to graze if necessary, usually in the mornings and evenings when temperatures are at their most stable and their are less predators active. Guinea pigs are crepuscular, i.e. most active at dawn and dusk. They often sleep or quietly browse hay during the middle of the day and can also be up sometimes during the night. That is the reason why pet piggies still enjoy tunnels and snug hideys so much and why a confined, dark space means safety to them!
Small core groups will settle not very far from each other (but are rather territorial over their small patch) but they comprehend themselves as members of the larger herd that gives them protection by numbers when on the move and during feeding.

Piggies are usually initially very wary of open spaces that leave them exposed to birds of prey as well as to ground predators; many don’t like being picked up for the same reason (even if they are happy with being cuddled on a lap), as that cuts very close to their prey animal instincts. They will often go “unresponsive” in the hopes that any predator (including a new owner) will lose interest and drop them.

Sows bring up their babies in a core group with a boar that has impressed them enough that want to associate with. It is the sows that choose who they want to father their babies, not the other way round! Fathers and the other sows are also involved in bringing up the babies and solicalising them. A large group can consist of a number of small core groups or baby crèches.
Bachelor boars are hanging loosely around; they are waiting for their big chance to attract a young sow or more. In the meantime, they can often hang out with congenial boar friend(s). They will try to mate with any young sows sneaking out from under daddy boar’s nose to found their own group (which prevents too much inbreeding).
The group will rest, move and eat/forage and guard their territory as a whole, which means that you cannot just stick in a new guinea pig or two into a cage and expect them to get on with each other! You have to always stage any bondings in neutral ground that doesn't bear the scent of other guinea pigs.

Because there is more food around a farmyard/pen, the territory of domestic guinea pig groups is a lot smaller than those of wild guinea pigs, who can roam an impressive distance between their grazing grounds and a safe place to sleep and rest. But they have retained many of their original instincts and social behaviours.

Guinea pigs have a very strict hierarchy, which they establish and reaffirm through dominance behaviour; this is what keeps a group together and makes it work. Boars across various core groups will work out a hierarchy amongst each other by rumble-strutting displays. The weaker guinea pigs will move away. The bottom guinea pig is as pivotal for the cohesion of the group as the top sow.
Boar fights are pretty rare where guinea pigs can move out of each other's way. That is why cage size is really important, especially with teenage boars which cannot get away from each other in a smaller cage and are forced to fight.
"First Lady" is usually a cunning, dominant sow in her prime on whose experience the survival of the group as a whole depends; the perks, like first choice of a safe sleeping space or privileged access to the best food, reflect the importance of her responsibilities.
Any boar needs to get on with all the higher ranked sows in his group, so he is often a peacemaker and diplomat and at best a co-leader and trailblazer.
Experienced mid-ranking sows will often rest at the entrances to a group home, taking over alert duties as snakes are also a danger to guinea pigs.

Newest and ongoing research is showing that guinea pigs have a much more complex society and communication system than previously assumed. Guinea pigs are every bit as clever as rats!

A guinea pig life cycle
Because of their roaming background, guinea pigs have comparatively few, large and fully developed babies after the longest - and therefore most risky - pregnancy of all rodents, excepting the closely related larger capybaras.
The in comparison large pups are born fully furred, with teeth and open eyes, and ready to keep up with the group within hours of being born. Babies can nibble on hay and adult foods straight away and are able to survive on their own from just a few days old (although very few actually will without support from other sows. Many guinea pig sows are thankfully not very fussy about whose babies they are nursing, so help is often at hand in a group)!

The nursing period is correspondingly very short. Mommy will start the weaning process from about 2-3 weeks onwards once the babies have shifted from mainly drinking mother's milk to eating mainly solids; weaning is usually finished by around 3-4 weeks.
Babies can start the next generation basically as soon as they are weaned (3 weeks boars, 4 weeks for sows) in order to make up for the long pregnancies, the comparatively high rate of births going wrong and the lower number of pups in each litter.

Pups learn to drink water and what is safe to eat from their elders, often snatching food from mommy’s or other adults' mouths to taste it. They explore the world by nibbling, as guinea pigs don’t have a vomit reflex and have to be careful around poisonous plants. They also learn the finer points of piggy group etiquette from older piggies as they grow up. As soon as the nursing period is over, mommies lose their protected status within the group and their pups are firmly pushed to the bottom of the hierarchy.

Guinea pigs are at the loudest and most vocal in the following months when they are at their most vulnerable to predators and can easily endanger the group as a whole through their inexperience. The constant chatter serves as a continuous update of their whereabouts and wellbeing for the group that often can’t see each other in the grass and has to stay in contact by their vocalisations.

Youngsters reach the teenage months from about 4-14 months old. Sows can have the odd very strong season during that period, but boars are more affected by hormonal spikes when their testicles descend and they develop their adult personality. This can lead to personality clashes, fights and even permanent fall-outs after deep bloody bites, especially if they live in pairs that are not character compatible and can’t get away from each other.

By 12-15 months old, guinea pigs generally stop growing (rex piggies mature a bit later) and settle down into a hormonally much more stable adulthood. They reach the peak of their lives at around 2-3 years old.

From about 4-5 years onwards, they are to be considered older citizens; you will notice that the older a guinea pig becomes, the more it is sleeping. Older guinea pigs also become a bit bonier, epsecially around the hips, but any large weight loss still needs to be vet checked. While some guinea pigs can experience a colour change of their fur throughout their life (usually a fading or darkening/dulling), they don't go gray or lose their coat in old age (the latter is always caused by a parasitic, fungal or health problem and requires vet care).
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