Someone Surrendered a Guinea Pig — Here's the Intake That Keeps It Alive

It comes in on a bag of colorful muesli, in a cage barely bigger than a shoebox, usually alone. Maybe a kid lost interest, maybe a family is moving. Or maybe it's "a couple" that turns out to be a boar and a sow who have been sharing a cage for two months — which means you may have just taken in a litter you cannot see yet. Guinea pigs are one of the animals rescues are quietly worst at, because almost everything the average owner "knows" about keeping them is wrong, and because a guinea pig will sit there looking fine right up until it crashes. The intake you run in the first 48 hours decides whether this animal lives a healthy seven years or dies of something preventable in three weeks.

Here's how to run it.

First, Separate and Sex Them

Before anything else — before the diet, before the health check — figure out how many animals you actually have and what sex they are. If there is an intact boar and a sow in the same cage, the clock is already running.

Guinea pigs hit puberty fast: sows can conceive at around two months old, boars a little after.¹ A sow can be pregnant well before her owner thought she was old enough, and nobody surrendering "two girls" has usually checked. Separate any possible mixed-sex pair immediately and sex each animal carefully. Mature boars have obvious scrotal pouches and large testes; gently pressing just above the genital opening on a boar will express the penis, while a sow's opening forms a Y-shape.¹ If you are not certain, get a vet or an experienced cavy person to confirm — misjudging this is how a rescue turns an intake of two into an intake of eight.

Assume any sow who was housed with a male is pregnant until proven otherwise, and treat her as the highest-priority animal in the intake. The next section is why.

Why an Accidental Pregnancy Is a Genuine Emergency

Guinea pig pregnancy is not like a cat's, and this is the fact that turns an "easy small-animal intake" into a case that needs a plan before you need it.

The two halves of a sow's pelvis are joined by a cartilage bridge called the pubic symphysis, which normally separates in late pregnancy to let the unusually large, well-developed pups pass. But if a sow has never given birth before she reaches roughly six to eight months of age, that cartilage calcifies and fuses permanently, narrowing the birth canal so much that natural delivery becomes difficult or impossible.² A first-time mother bred after that window is a strong candidate for dystocia — an obstructed birth that, without an emergency caesarean, kills the sow and the litter.²

On top of that, late pregnancy carries the risk of pregnancy toxemia, a metabolic collapse most common in overweight sows in the last two weeks before birth. The signs run from loss of appetite and weakness to incoordination, laboured breathing, coma and death.³

The practical upshot: if you suspect a pregnant sow — especially one you think was bred late, or who is overweight — get her in front of an exotics vet early, and find out where the nearest emergency caesarean is available before you need it. Do not wait to see how she goes.

Assume It's Sick Until It Proves Otherwise

Guinea pigs are prey animals, and prey animals are built to look healthy. A cavy will keep eating, keep moving, keep acting normal while a serious problem builds underneath, because over evolutionary time the ones that showed weakness got picked off. A refusal to eat is often the first sign you'll get, and by then the clock is already running.⁴

So the master signal at intake is the same one it is for rabbits: appetite and droppings. Offer hay the moment the animal arrives and watch. Is it eating? Are there normal fecal pellets in the enclosure within a few hours? A guinea pig that stops eating or stops pooping is not a "see how it looks in the morning" case — it's GI stasis, a digestive emergency where the gut slows or stops, and it can progress to death within 24 to 48 hours. The common guidance is blunt: if a guinea pig hasn't eaten or passed stool in 12 hours, treat it as an emergency.⁵

Weigh every animal at intake and then regularly. In a species built to hide illness, the scale is your best early-warning system — weight loss shows up before the animal looks unwell. Write down what you see, with the time. "Ate hay 3pm, several droppings by 6pm" is a baseline you'll be grateful for if the animal goes quiet on day four.

Fix the Diet on Day One — It's Almost Certainly Wrong

Whatever this guinea pig came in eating, it was probably making it sick, because the pet-store default — a bowl of colorful muesli and a couple of carrots — is close to the worst possible diet. The muesli-style mixes let an animal pick out the sugary bits and leave the rest, which is a poor fit for a hay-first eater.

The foundation of a healthy guinea pig is unlimited grass hay, available free-choice all the time. Hay should make up roughly 85% of the daily diet, with a small ration of plain pellets (about 10%) and fresh leafy greens (about 5%).⁶ There are two separate reasons hay is non-negotiable. First, it's the fiber that keeps the gut moving and prevents the stasis above. Second, guinea pig teeth never stop growing — the cheek teeth and incisors grow continuously, on the order of 1 to 2 mm a week — and the only thing that wears them down is the sideways grinding chew that long-strand hay forces. Feed mostly pellets and grain and the teeth wear unevenly, overgrow, and can eventually trap the tongue. Guinea pigs with established dental disease may need corrective procedures every one to two months for the rest of their lives, so preventing it with hay from day one is enormously cheaper than treating it.⁶

So your day-one diet is simple: unlimited grass hay (timothy or orchard for adults, not alfalfa), fresh water, a measured portion of guinea-pig-safe greens, and a small ration of plain timothy-based pellets — no seeds, no dried fruit, no colored bits. Then watch that the animal is actually eating the hay. A pig that stops chewing hay is often telling you its teeth hurt.

Supplement Vitamin C — Every Single Day

This is the one that catches even experienced dog-and-cat rescues off guard. Guinea pigs, almost uniquely among common companion animals, cannot make their own vitamin C — they lack the enzyme, exactly like humans do — so it has to come from the diet every day. Without it they develop scurvy, and the symptoms read like a checklist of things you might otherwise misdiagnose: rough coat, loss of appetite, difficulty eating, a stiff or limping gait, swollen or painful joints, poor wound healing, diarrhea, weight loss, and greater susceptibility to other infections.⁷

Dose it properly. A healthy adult needs roughly 10 mg of vitamin C per kilogram of body weight daily — about 20 to 25 mg a day for most adults, and 30 to 40 mg for a growing, sick or pregnant animal.⁸ Pellets are often sold as "fortified," but the vitamin C in them degrades quickly once the bag is opened and exposed to light and air, so you cannot rely on pellets alone. Provide it directly: vitamin-C-rich greens like bell pepper daily, plus a dedicated supplement — a tablet or liquid dosed by weight, not the drops that dissolve in the water bottle, which degrade fast and make the water taste bad enough that the animal drinks less.⁸

Put the daily C dose on the same care record as feeding, because "did anyone give the vitamin C today?" is exactly the kind of thing that falls through the cracks in a busy foster home. A surrender that arrived on a seed-and-corn mix has almost certainly been running a deficit already.

Quarantine, Then Look for the Usual Suspects

Guinea pigs from pet stores, homes, or online listings should be quarantined for two to three weeks before going anywhere near your resident herd, with separate handling.⁹ Quarantine also protects the incoming animal: a stressed, immune-compromised new arrival is exactly who catches whatever your resident group is carrying. Use the window as your observation period, and examine for the conditions that dominate guinea pig rescue.

Skin mites. Trixacarus caviae is a burrowing mange mite that lives inside the skin. Guinea pigs frequently carry it with no symptoms at all, and it is precisely the stress of being surrendered and moved that triggers an outbreak — so an animal that looks clear on arrival can erupt a week later. It causes itching severe enough that affected pigs scratch themselves raw and can have seizures triggered by the pain, and untreated cases can be fatal.⁹ Any pig that is frantically itchy, losing hair, or crusty along the back and flanks needs a vet and treatment — an antiparasitic such as ivermectin or a modern isoxazoline — and its cagemates almost certainly need treating too.¹⁰ Many rescues simply treat every incoming guinea pig prophylactically rather than risk seeding it through the whole population.⁹ Never write off intense scratching as "just dry skin."

Respiratory infection. Upper respiratory infections are among the most common problems in the species, driven by organisms like Bordetella and Streptococcus.¹¹ Listen for sneezing, nasal or eye discharge, clicking or crackly breathing, or a pig that is hunched and eating less. Respiratory disease moves fast in a small animal and warrants a prompt vet visit, not a wait-and-see.

Dental disease. Because the teeth never stop growing, malocclusion is a recurring problem.¹¹ The tells are drooling, a wet chin, dropping food, weight loss, or a pig that wants to eat but backs off the hay. This needs a vet with the equipment to examine and file the back teeth.

Bumblefoot. Pododermatitis — swollen, scabbed, ulcerated footpads — develops on wire flooring and in dirty caging.¹¹ Check the soles at intake, and house pigs on solid floors with clean, soft bedding.

Ovarian cysts. In intact sows over about two years old, ovarian cysts are commonly reported, with one clinical dataset finding them in more than 75% of older intact females.¹¹ The classic sign is symmetrical, non-itchy hair loss along both flanks, which is easy to confuse with mites until you notice the skin underneath is calm and unscaling. It is a reason to consider spaying and a good thing to flag to any future adopter.

Also watch for ringworm, which is a fungus and transmissible to humans — wash hands or glove up.⁹

Never Adopt Out Just One

Guinea pigs are herd animals. In the wild they live in groups and depend on constant companionship; kept alone, they are prone to stress and depression. The RSPCA advises keeping every guinea pig with at least one other friendly guinea pig unless a vet or behaviorist says otherwise, and a stable group is often two or three sows with a neutered boar.¹² Switzerland went further and made it illegal to keep a single guinea pig at all, treating solitary housing as a form of neglect.¹³

You don't have to adopt them out in the exact pair that came in, but a lone guinea pig should be bonded with a compatible companion, and your adoption policy should reflect that. A bonded pair is also easier to place well, because you are handing the adopter a stable social unit instead of an animal that will pine. Pair deliberately, after quarantine and health clearance, and introduce on neutral ground with plenty of hay and hiding spots.

This is also the other reason sexing and neutering matter up front: intact males and females left together breed relentlessly, and a solo surrender isn't really "done" until it is safely bonded.

Keep One Record Per Animal From Day One

The thing that quietly breaks small-animal rescue is lost information. A guinea pig passes through surrender, intake, quarantine, vetting, foster, and adoption, and at every handoff the knowledge — when it last ate normally, what its droppings looked like, whether it got its vitamin C today, the mite-treatment date and its repeat, that it's bonded to the other sow and shouldn't be split — tends to live in one person's head and evaporate. With an animal whose first symptom of a fatal problem is "ate a little less today," that history is the difference between catching stasis on day one and finding the animal collapsed on day three.

Keep one record per guinea pig from the moment it arrives: intake date and circumstances, weight and subsequent weights, sex and suspected pregnancy status, daily appetite and droppings, vitamin C given, quarantine and mite treatment dates, vet notes, diet, bond partner, and temperament. This is exactly the kind of per-animal record Pawsies is built to hold — one profile per animal with medical events and daily notes attached, viewable by your whole team from a phone, so the history follows the animal to its next home instead of dying in a notebook. A binder works too. What matters is that the next person doesn't start from a muesli bag and a guess.

The Short Version

Sex them before anything else. Sows can conceive from two months, and a sow bred after six to eight months has a permanently fused pubic symphysis and a real risk of obstructed birth that kills her and the litter without an emergency caesarean.¹² Assume any sow housed with a male is pregnant and get her in front of an exotics vet early. After that the killers are ordinary: a guinea pig that hasn't eaten or passed stool in 12 hours is a GI stasis emergency that can progress to death in 24 to 48 hours.⁵ Feed roughly 85% grass hay, 10% plain pellets, 5% greens, with hay free-choice always.⁶ Supplement vitamin C daily — about 10 mg per kilo, so 20–25 mg for a typical adult and 30–40 for one that's growing, sick or pregnant — and never through water-bottle drops.⁸ Quarantine two to three weeks and treat for mites.⁹ Never adopt out just one.¹² And weigh them: in an animal built to hide illness, the scale notices before you do.

A guinea pig can live five to seven years or more with the right care. The one someone handed you in a shoebox didn't fail — it was set up to. A careful intake — sexing before anything else, treating a possible pregnancy as an emergency, assuming illness, fixing the diet, supplementing vitamin C daily, never leaving it alone, quarantining before contact, and writing it all down — is what turns one more impulse-buy cavy into the home where it finally stays.

This is a field guide written from rescue experience, not veterinary advice, and nothing here replaces a diagnosis. A guinea pig with signs of illness, a suspected pregnancy, or a severe mite infestation needs an exotics-experienced veterinarian. Any product or dose named should be confirmed with your vet against what is licensed and available where you are. If an animal is going downhill, call — don't wait until you've finished reading.