Guinea Pig Diet: Vitamin C Sources, Calcium and a Daily Feeding Plan

This page is for guinea pig owners who want to check that the daily vegetable cup actually covers vitamin C, without overloading on calcium. It goes further than the diet row on the guinea pig care guide. You’ll find figures for common vegetables, a food table, and what changes if a guinea pig has had bladder stones.

Vitamin C and calcium in common vegetables

Guinea pigs need 10–50 mg of vitamin C a day, depending on age, health, stress and pregnancy (VCA). The best vegetables are high in vitamin C and low in calcium. The figures below are per 3.5 oz (100 g) of raw vegetable.

Vegetable	Vitamin C	Calcium	Verdict
Parsley	133 mg (USDA FoodData Central)	138 mg (USDA FoodData Central)	High in both. Sources disagree on how often to feed it (see below)
Red bell pepper	128 mg (USDA FoodData Central)	7 mg (USDA FoodData Central)	Best all-round daily choice
Kale	93 mg (USDA FoodData Central)	254 mg (USDA FoodData Central)	Treat only (RSPCA). High calcium (Merck)
Green bell pepper	80 mg (USDA FoodData Central)	10 mg (USDA FoodData Central)	Good daily choice
Romaine lettuce	4 mg (USDA FoodData Central)	33 mg (USDA FoodData Central)	Safe filler, but adds almost no vitamin C

In practice, a 1/3 oz (10 g) strip of red pepper gives about 13 mg of vitamin C, which covers the bottom of VCA’s range on its own. Romaine is a safe base for the cup, but it can’t be your vitamin C source.

Where sources disagree. The RSPCA lists parsley as a vegetable to feed often. Merck groups parsley with kale and spinach as high-calcium greens that “should not be given often”. For a guinea pig that has had stones, MSPCA-Angell advises giving kale and parsley sparingly. Citrus is a second disagreement. VCA suggests orange and kiwi as occasional high-vitamin-C fruits, while the RSPCA puts citrus fruits on its “can’t eat” list. If you want to avoid the question altogether, peppers give the vitamin C without either problem.

Daily plan for one adult guinea pig

Item	Amount	Notes
Grass hay (timothy, orchard) and grass	Unlimited, 80–90% of the diet (PDSA)	In a rack to keep it clean (Merck)
Fresh vegetables	About 1 cup a day (PDSA)	Include a high-vitamin-C item every day (VCA)
Guinea pig pellets	About 2 tablespoons (1/8 cup) (Merck)	Give a fresh portion daily rather than topping up (RSPCA)
Fruit	A small piece, occasionally (VCA)	Too much sugar can cause serious diarrhoea (VCA)
Water	Always available, changed at least daily (VCA)	Nothing added to it (Merck)

Pellets lose vitamin C as they age. VCA says to use them within 90 days of the manufacture date. Exposure to air speeds up the loss (RSPCA), so keep the bag sealed. Alfalfa-based pellets suit young, growing or pregnant guinea pigs, and adults do better on timothy-based pellets with less calcium (Merck). If the diet is pellets with stable vitamin C, plus timothy hay and some leafy greens, VCA says separate supplements aren’t needed.

Safe, limit and never

Food	Status	Source
Bell peppers, romaine, gem lettuce, cucumber, celery	Feed often	(RSPCA)
Green and red leaf lettuce, endive, carrot tops, beet greens, coriander	Safe	(VCA)
Parsley	Often for the RSPCA, sparingly for Merck	(RSPCA; Merck)
Broccoli, spinach, kale	Treat, a few times a week	High in sugar or calcium (RSPCA)
Carrot, apple, pear	Treat	About a quarter of an apple (RSPCA). Small amounts only (Merck)
Iceberg lettuce	Never	Mostly water (VCA; Merck)
Potato, garlic, avocado, coconut	Never	(RSPCA)
Oats, seeds, nuts, dry cereals	Never	Too high in carbohydrate and fat (VCA)
Lawnmower clippings	Never	Upset digestion (RSPCA)

Calcium and bladder stones

Stones are common in guinea pigs and affect both sexes. Calcium carbonate stones make up 90% of those identified (MSPCA-Angell). Merck links excess calcium from greens such as parsley, kale and spinach to stone formation. MSPCA-Angell describes medical management as “often unrewarding”. Surgery is the only effective immediate treatment, and stones commonly come back afterwards.

For a guinea pig at risk, MSPCA-Angell’s dietary priorities are:

• More water. Offer water from a bottle, which tends to increase how much they drink. Serve low-calcium greens soaked in water.
• Less calcium. Feed kale and parsley sparingly, give adults timothy pellets rather than alfalfa (Merck), and lean on peppers for vitamin C.
• Watch for signs. Blood in the urine or straining to pass it needs a vet. Red urine can also be harmless pigment from carrots or spinach (MSPCA-Angell).

Mistakes that cause problems

• Topping up last week’s pellets. Vitamin C breaks down over time (RSPCA), so a full bowl can still leave a guinea pig short and at risk of scurvy (VCA).
• Adding vitamin C to the water bottle. Merck says not to add supplements to drinking water. Pellets used within their date and a high-vitamin-C vegetable every day do the job.
• Building the cup around lettuce. Romaine has 4 mg of vitamin C per 100 g (USDA FoodData Central). A lettuce-heavy cup can look generous and still supply very little.
• Heavy daily kale or parsley for a stone-former. Both are high in calcium (USDA FoodData Central), and MSPCA-Angell advises giving them sparingly.
• Too many pellets, not enough hay. Merck links this to diarrhoea, painful gas and bloating. Too little hay also means less tooth wear, and Merck lists that as a cause of dental disease.

For how this compares with rabbit feeding, see the rabbit diet guide. For other species, see pet nutrition fundamentals.