Guinea Pig Diet: Hay, Vitamin C and Safe Vegetables
10 min readA guinea pig's diet rests on three pillars: unlimited hay, which should make up 85 to 90% of its intake, vitamin C every day, because it cannot make its own, and about a cup of fresh, varied vegetables a day. Guinea pig pellets are given in small amounts; fruit and treats should remain rare.
Written by the Haynest team. Researched from veterinary recommendations and guidance from animal welfare organisations.
Guinea pig diet at a glance
The guinea pig is a herbivore that nibbles day and night. Its diet is built like a pyramid: lots of fibre, a little fresh food, very little sugar.
| Food | Reference amount | How often |
|---|---|---|
| Hay (and fresh grass) | Unlimited, 85 to 90% of the diet | At all times |
| Vegetables and leafy greens | About one cup (250 ml), 5 to 6 different kinds | Every day |
| Guinea pig pellets | About one tablespoon per adult | Every day |
| Fresh water | Unlimited | Check twice a day |
| Fruit and treats | A very small amount | Occasionally |
Hay for guinea pigs: the foundation of the diet
Hay is vital for two reasons:
- Its teeth grow continuously, throughout its life. Chewing hay wears them down and keeps them at the right length.
- Its gut needs fibre. Without it, digestion can slow down or even stop: this is gut stasis, which can be life-threatening.
According to the PDSA, hay and grass should make up 85 to 90% of its diet. A rule of thumb from the MSD Veterinary Manual: a guinea pig should eat roughly its own body size in hay every day. Serve it in a hay rack and replace it daily. For an adult, choose a grass-based meadow hay. Fresh grass is a good complement, as long as it is picked by hand: lawn mower clippings ferment quickly and make guinea pigs ill.
What about alfalfa (lucerne)? This legume is richer in calcium than grasses. Alfalfa-based foods are mainly suited to growing youngsters and pregnant females; for an adult, choose grasses instead.
A versatile, high-fibre hay to keep in the hay rack without limit.
Our most palatable hay, harvested on the Crau plain: a favourite with fussy eaters.
The same hay suits both rabbits and guinea pigs: our guide Which Hay Is Best for Your Rabbit? applies to guinea pigs too.
Vitamin C: a daily need for guinea pigs
Like humans, guinea pigs cannot make their own vitamin C: they need to get it from their food every day. It is essential for their skin, joints and blood vessels.
How much vitamin C per day?
According to the MSD Veterinary Manual, an adult needs 10 to 25 mg per kilo of body weight per day, and 30 mg per kilo or more for a growing youngster, a pregnant or nursing female, or a sick animal. For an adult weighing about one kilo, that means 10 to 25 mg a day. The vets at VCA work with 10 to 50 mg a day, depending on age, health, stress and pregnancy.
Where to find it
In fresh vegetables and fortified pellets. Among the richest vegetables, veterinary sources list bell pepper, parsley, kale, spinach, tomato, broccoli and red cabbage. The vitamin C in pellets, however, breaks down over time and with heat, light and humidity: store them somewhere dry, cool and dark, and use them within three months of purchase (PDSA).
Vitamin C content varies enormously from one vegetable to another. According to the French food composition table Ciqual (ANSES, 2025), 17 g of red bell pepper provides as much vitamin C as 500 g of romaine lettuce, and red bell pepper contains more than four times as much as green. Romaine, cucumber and celery are still useful for variety and water, but they cover almost none of the need.
What about vitamin C in the water?
This is not recommended: vitamin C breaks down in light, and the taste of the drops can put your guinea pig off drinking. With vitamin C-rich vegetables every day, a supplement is generally unnecessary; if in doubt, ask your vet for advice.
Signs of vitamin C deficiency (scurvy): loss of appetite, dental problems, swollen joints, limping, bleeding under the skin, a rough coat, weight loss, diarrhoea. See a vet promptly, ideally an exotic-pet vet.
Safe fruit and vegetables: how much?
PDSA vets recommend about one cup of vegetables and leafy greens per guinea pig per day, with at least 5 to 6 different kinds, several of them rich in vitamin C. Variety matters: in a 2025 study cited by the MSD Veterinary Manual, guinea pigs that received at least 7 kinds of plants developed markedly fewer urinary stones. Introduce each new food gradually and remove fresh leftovers after a few hours.
| Vegetable or green | Why it's useful | How often |
|---|---|---|
| Bell pepper | Very rich in vitamin C | Often, in rotation |
| Romaine lettuce, little gem lettuce | A staple green, readily eaten | Often, in rotation |
| Cucumber, celery | Low in sugar, add variety in texture | Often, in rotation |
| Carrot tops, freshly picked grass | Popular greens | Regularly |
| Parsley | Rich in vitamin C, but also in calcium | A few sprigs, not too often |
| Tomato (the fruit only) | Vitamin C, low in sugar | Small amounts; never the leaves or stems |
| Broccoli, kale, spinach | Vitamin C, but calcium (kale, spinach) or gas (broccoli) | Small amounts, a few times a week |
| Carrot | Higher in sugar | Small pieces, a few times a week |
Frequencies based on guidance from the RSPCA and the MSD Veterinary Manual.
Pellets: made for guinea pigs and properly measured
Pellets complement hay but never replace it. PDSA vets recommend about one tablespoon per adult per day. Guidance varies between sources: follow the manufacturer's instructions, and ask your vet for advice for a youngster, a pregnant female or an underweight animal.
- Never rabbit pellets: they don't contain enough vitamin C.
- Grass-based for an adult, such as timothy: they are lower in calcium than alfalfa-based pellets.
- Uniform in shape and colour, so your guinea pig can't pick out its favourite bits.
- A fresh portion every day, without topping up the previous day's bowl. A tip from the PDSA: scatter it around the enclosure so your guinea pig has to search for it.
Water, fruit and treats: good habits
Water must be clean and available at all times. The RSPCA advises checking the water supply twice a day. A drinking bottle stays cleaner than a bowl: clean it every day, and don't add anything to the water.
Fruit is high in sugar: too much can upset the gut flora and cause severe diarrhoea. Apple (without the pips, which are toxic), pear, strawberry, blueberry, kiwi or melon can be given in very small amounts; as a guide, the RSPCA suggests a quarter of an apple, a few times a week.
Treats: according to the PDSA, one treat every one to two weeks is enough, avoiding brightly coloured, very sugary products. Our dried apple or carrot chips (see our natural treats) contain natural sugars, concentrated by drying: for a guinea pig, a small piece, rarely. Our guide to treats, written for rabbits, doesn't apply to guinea pigs as it stands.
Foods guinea pigs must never eat
According to the RSPCA, the PDSA and VCA vets, never give:
- potato (including the skin), onion, garlic, chives, mushrooms;
- avocado, rhubarb, coconut, citrus fruit;
- tomato leaves and stems, apple pips;
- iceberg lettuce, which is mostly water;
- seeds, nuts, oats and dry cereals, which are too high in carbohydrates and fat;
- lawn mower clippings, and plants you can't identify or that were picked in a sprayed area.
If you think your guinea pig has eaten something toxic, call your vet straight away.
A typical day of feeding your guinea pig
- In the morning — remove soiled hay, fill the hay rack generously, check the water.
- Pellets — a fresh portion, about a tablespoon, scattered around the enclosure.
- A first serving of vegetables — for example bell pepper, a romaine leaf and a few carrot tops.
- During the day — unlimited hay and, if possible, a handful of freshly picked grass.
- In the evening — the rest of the vegetables (cucumber, celery, a sprig of parsley), remove fresh leftovers, a full hay rack for the night and a second water check.
- Regular weigh-ins — weight loss can be a sign of illness; weight gain, of too many pellets or vegetables.
Common mistakes to avoid
- Seed mixes: they encourage selective eating and are too rich for a herbivore.
- Too much fruit: even natural fruit is sugary and upsets digestion.
- Too much calcium: parsley, kale or spinach too often, alfalfa pellets for an adult. Excess calcium can contribute to bladder stones.
- Sudden changes: guinea pigs don't adapt well to new foods and may refuse to eat. Make any transition over two to four weeks, gradually mixing the old and new food.
Emergency: a guinea pig that stops eating is at risk of gut stasis, which can be life-threatening. If its appetite, water intake or droppings change (absent, fewer or softer), contact a vet immediately, ideally an exotic-pet vet.
Frequently asked questions
How much vitamin C does a guinea pig need per day?
An adult needs 10 to 25 mg per kilo of body weight per day, and 30 mg per kilo or more during growth, pregnancy, nursing or illness. Vitamin C-rich vegetables and fresh pellets are generally enough.
Can a guinea pig eat rabbit food?
Hay, yes: the same good-quality hay suits both. Rabbit pellets, no: they don't contain enough vitamin C.
How many vegetables should a guinea pig eat per day?
About one cup per guinea pig, with at least 5 to 6 different kinds. Keep an eye on its weight and adjust.
My guinea pig eats its droppings: is that normal?
Yes. It eats special soft droppings called caecotrophs: this is part of its digestion and lets it recover all the nutrients from its food.
In summary
Unlimited hay, a cup of varied, vitamin C-rich vegetables, a small spoonful of guinea pig pellets and fresh water: that is the basic diet of a healthy guinea pig. Fruit and treats stay rare, and every change is made gradually.
To find out more: how to choose good hay, for your rabbit and your guinea pig alike.
Sources
- RSPCA — What to feed a guinea pig
- PDSA — Your guinea pig's diet
- MSD Veterinary Manual — Diet for a Guinea Pig
- MSD Veterinary Manual — Nutritional Problems of Guinea Pigs
- MSD Veterinary Manual (professional version) — Housing and Nutrition of Guinea Pigs
- VCA Animal Hospitals — Feeding Guinea Pigs
- ANSES — French food composition table Ciqual 2025
Photos: cover, patrice schoefolt (Pexels); guinea pigs and romaine, Magda Ehlers (Pexels); meadow, Haynest.
This article is for information only and does not replace a vet's advice. If you have any doubts about your guinea pig's health, consult a professional, ideally an exotic-pet vet.
