Guinea pig diarrhoea: is it really diarrhoea, what causes it, and the first 24 hours

Quick answer

The first question is not what caused it. It is whether this is true diarrhoea or squashed caecotrophs, because the two lead to completely different actions.

Most soft droppings owners find in a guinea pig cage are not diarrhoea. They are caecotrophs, the soft nutrient-rich pellets a guinea pig normally eats directly from itself, left behind because the animal could not reach.

True diarrhoea in a guinea pig is uncommon and it is serious. It means unformed or watery faeces, a soiled wet rear end, and usually a guinea pig that is not itself. In a hindgut fermenter of this size, that combination can be fatal within a day or two.

• Look for normal firm droppings alongside the soft ones. If both are present, you are usually dealing with uneaten caecotrophs, not diarrhoea.
• Watery faeces plus a guinea pig that has stopped eating is an emergency, not a wait-and-see.
• The commonest avoidable cause of fatal guinea pig diarrhoea is the wrong antibiotic.
• Never stop offering hay. A guinea pig gut that stops moving is a separate emergency that develops within hours.
• Weigh the animal now and write the number down. Weight is the measurement that will tell you whether things are improving.

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Several common antibiotics kill guinea pigs.

A guinea pig's gut is run by gram-positive anaerobic bacteria. Antibiotics that target gram-positive organisms wipe out that population and allow clostridial species to overgrow and release toxin. The result is enterotoxaemia: severe diarrhoea, collapse and frequently death within one to three days.

The classes involved include penicillins such as amoxicillin and ampicillin, cephalosporins, lincomycin, clindamycin, erythromycin and tylosin. This applies to oral, injectable and in some cases topical preparations, including some ear and eye drops.

If your guinea pig has been prescribed anything and then develops diarrhoea, contact the prescribing vet immediately and say so. Never give a guinea pig an antibiotic prescribed for another animal or another species, and always confirm that a vet treating your guinea pig is familiar with the species.
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Decide in 60 seconds

Caecotrophs, and why this distinction comes first

Guinea pigs extract nutrition in two passes. Fibrous food ferments in the caecum, producing a soft, moist, strongly smelling pellet packed with B vitamins and microbial protein. The animal takes these directly from the anus and eats them, usually while curled up and often unobserved.

That means a healthy guinea pig produces two kinds of dropping and you should normally only find one of them. Firm, dry, oval pellets in the bedding are the finished product. Soft, sticky, clustered pellets in the bedding are caecotrophs that were not consumed.

When you find caecotrophs, the question is why the animal did not eat them. The answer is almost always mechanical or medical rather than digestive.

It cannot reach.
Obesity, arthritis, spinal pain, a heavily pregnant sow, or a long coat matted around the rear all physically prevent it.

It is not curling up.
Pain anywhere, particularly abdominal or dental pain, stops the posture required.

It does not want to.
An over-rich diet, particularly too much fresh food or too many pellets, produces more caecotrophs than the animal needs, and it leaves the surplus. This is the one dietary cause, and the fix is more hay and less of everything else.

It cannot chew them.
Dental disease. A guinea pig with overgrown molars often has a wet chin and drops food.

The tell that separates this from diarrhoea is the presence of normal droppings at the same time. Diarrhoea replaces normal droppings; uneaten caecotrophs sit alongside them.

True diarrhoea: what causes it

Antibiotic-associated enterotoxaemia.
Covered above. It is first on this list because it is the most preventable and the most lethal.

Sudden or excessive fresh food.
A large volume of new greens, wet grass, or fruit shifts caecal fermentation. The classic pattern is soft faeces within a day of a diet change, in an otherwise bright animal, resolving when the food is withdrawn and hay is increased.

Spoiled or contaminated food.
Mouldy hay, wilted or fermenting greens left in the cage, or greens carrying pesticide residue. Mould in hay is a genuine hazard and is often missed because owners assess hay by appearance rather than by smell.

Low fibre intake.
A guinea pig eating mostly pellets and vegetables rather than hay has a caecum that is not getting the long fibre it needs, and its gut function becomes unstable.

Coccidia and other parasites.
Eimeria caviae is a common cause in young guinea pigs and in newly acquired animals, especially those from crowded conditions. It typically produces diarrhoea in a young animal that is also failing to gain weight.

Bacterial infection.
Salmonella, certain E. coli strains, Yersinia and clostridial species. These are more likely in new arrivals, in groups where more than one animal is affected, and where hygiene or wild rodent contact is a factor.

Cryptosporidium.
Mainly in young guinea pigs, causing persistent diarrhoea and poor growth.

Underlying disease.
Dental disease that prevents hay eating, liver or kidney disease, and any painful condition that reduces food intake can all destabilise the gut secondarily. In an older guinea pig with diarrhoea and no obvious dietary cause, look for the primary problem.

Toxins.
Houseplants, garden plants, treated lawn clippings, and cleaning products residue.

Daily weight is the only objective measure you have at home. Same scale, same time of day, written down.

Staging, and why it moves fast

Mild.
Droppings softer than usual but still holding shape, produced in normal numbers. The guinea pig is eating hay, active, and interested in food. Weight steady.

Moderate.
Droppings unformed, fewer of them, some soiling of the rear. Appetite reduced. The animal is quieter than usual. Weight starting to drift down.

Severe.
Watery faeces, marked soiling, few or no formed droppings. The guinea pig is hunched with the coat standing up, eyes partly closed, not eating, and ears and feet feel cold. Weight loss obvious.

Collapse.
Weak, unresponsive, cold, sometimes with abdominal distension. This animal needs intensive veterinary support.

The progression between these stages can happen inside a day. The reason is scale: an animal of this size loses a large proportion of its total body water very quickly, and fluid loss, falling body temperature and gut stasis reinforce one another. On top of that, a guinea pig that stops eating begins to accumulate its own set of problems within hours, regardless of what started it.

This is why "wait and see for a couple of days" is the wrong instinct for a guinea pig even though it would be reasonable for a dog.

The first twenty-four hours at home

Do these while you arrange a veterinary appointment, not instead of one.

Weigh the animal now.
Then again at the same time each day. A falling weight over twenty-four hours is the clearest signal that things are worsening.

Keep hay unlimited.
This is not negotiable. Fibre is what the caecum needs and gut movement is what you are trying to preserve. Never fast a guinea pig.

Remove fresh food temporarily.
Withdraw vegetables, fruit and grass while the gut settles, but keep a reliable vitamin C source going, because guinea pigs cannot make their own and an unwell animal needs it more, not less. Ask the vet what to use.

Keep the animal warm.
A guinea pig with diarrhoea loses heat fast. Provide a covered warm area it can move away from, never a heat source it cannot escape.

Keep water available and check it is being used.
Note whether the bottle level is dropping.

Clean and dry the rear end.
Gently, with warm water and no soap, then dry thoroughly. A wet soiled perineum causes scald and, in warm weather, attracts flies. Flystrike in a guinea pig is a rapid emergency.

Collect a fresh sample.
Put a fresh dropping in a clean sealed container. This is the single most useful thing you can bring.

Syringe feed only on advice, and only if the animal is not eating.
A recovery formula for herbivores is what a vet will direct you to. Never syringe feed a collapsed or cold animal without instruction, because aspiration is a real risk.

Separate carefully.
If more than one animal is affected, or if a new animal recently arrived, mention it. If you separate a bonded pair, keep them within sight and smell of each other.

A coat standing on end, half-closed eyes and a hunched outline are what a guinea pig in trouble looks like.

What changes by age, group and season

Young and newly acquired guinea pigs.
Infectious causes rise sharply. Coccidia and cryptosporidia are more likely, and diarrhoea in a young animal that is not gaining weight needs a faecal examination rather than a dietary adjustment.

More than one animal affected.
This shifts the likelihood strongly towards an infectious cause or a shared food problem, and it changes the hygiene advice for the whole enclosure.

Older guinea pigs.
Look for the underlying disease. Dental problems, arthritis preventing caecotrophy, and organ disease are all likelier explanations than a dietary indiscretion.

Pregnant sows.
A late-pregnancy sow may leave caecotrophs simply because she cannot reach, and she is also at risk of pregnancy toxaemia, which can look like a general decline. Any unwell pregnant sow is urgent.

Warm weather.
Flystrike risk on a soiled rear end turns a manageable problem into a critical one within a day. Check the rear end twice daily in warm months.

Spring grass.
A sudden switch to large volumes of lush young grass is a classic trigger. Introduce grass in small amounts over a week or more.

What the vet will ask for

• A fresh faecal sample, ideally from that day.
• Current weight and the trend over the last week.
• The exact diet: hay type and how much is eaten, pellet brand and quantity, every vegetable and fruit given, and anything new.
• Any medication given to this animal or its cage mates in the last month, including drops and topical products.
• Whether other animals in the group are affected.
• Whether any new guinea pig has been introduced recently, and when.
• Access to grass, garden plants, houseplants or lawn clippings.
• Dental history and whether the animal is eating hay normally.
• Water intake, and whether the bottle level is dropping as usual.

What never to do

Do not fast a guinea pig. Withholding food to rest the gut is dog and cat advice and it is dangerous here.

Do not give an antibiotic that was not prescribed for this guinea pig by a vet who knows the species.

Do not give loperamide, kaolin or other human anti-diarrhoeal preparations.

Do not stop the vitamin C source because the animal is unwell.

Do not bathe a guinea pig to clean a soiled rear. Spot clean with warm water and dry thoroughly. A full bath in a compromised animal causes chilling.

Do not delay because the guinea pig is still eating. Appetite is one of the last things to go and one of the least reassuring signs in this species.

Do not treat a soiled rear end in warm weather as a cosmetic problem.

Do not change the diet drastically as a home remedy. Increase hay, remove fresh food, and let the vet direct the rest.

Recovery is measured by weight and appetite returning, not by the first firm dropping.

When to get help

Go immediately for watery faeces with loss of appetite, cold ears and feet, a hunched posture, weakness, abdominal distension, or diarrhoea in an animal that has had any antibiotic recently.

Go the same day for unformed faeces in an animal that is still eating, any diarrhoea in a young or newly acquired guinea pig, a soiled wet rear end in warm weather, or diarrhoea affecting more than one animal.

Book within a few days for persistent uneaten caecotrophs in a bright animal, so that the reason the animal cannot reach or does not want to can be identified before it becomes a scald or a flystrike problem.

Choose a practice that regularly treats guinea pigs. The single most important decision in a guinea pig with diarrhoea is which drugs are safe to use, and that is species knowledge rather than general small animal knowledge.