What Do Guinea Pigs Eat? Daily Diet and Vitamin C Guide

Guinea pigs are herbivores with a few unusual needs. Their teeth never stop growing, their gut needs a steady supply of fiber, and, like people, they cannot make their own vitamin C. Get those three things right and you have covered the most important parts of their diet.

The guinea pig diet at a glance

These are general amounts for healthy adults. Ask your vet for advice for young, pregnant, older, or overweight guinea pigs.

Hay: the most important food

Hay should make up most of what your guinea pig eats. It keeps the gut moving and grinds down teeth that grow all the time. A guinea pig without enough hay can develop overgrown teeth, which make eating painful.

• Offer fresh grass hay every day, and refill when it gets low or dirty.
• Timothy, orchard grass, and meadow hay are good choices for adults.
• Alfalfa hay is richer in calcium and protein. It suits young, pregnant, or nursing guinea pigs, but too much can contribute to bladder stones in adults.

Vitamin C: the daily must

According to the MSD Veterinary Manual, guinea pigs need at least 10 mg of vitamin C per kilogram of body weight each day, and pregnant females need about 30 mg per kilogram. Since most adult guinea pigs weigh around 1 kg, that works out to roughly 10 mg a day for a typical adult, or about 30 mg for a pregnant female.

Without enough vitamin C, guinea pigs develop scurvy. Signs include:

• Loss of appetite and weight loss
• Rough coat
• Swollen, painful joints and limping
• Bleeding gums or bleeding under the skin
• Diarrhea and weakness

Good vitamin C vegetables

The MSD Veterinary Manual lists these foods as rich in vitamin C:

• Bell peppers (red, yellow, or green)
• Broccoli
• Parsley
• Kale
• Red cabbage
• Turnip greens
• Oranges and strawberries (as treats, because of the sugar)

Bell pepper is a favorite with many owners because it is high in vitamin C and most guinea pigs love it.

Why pellets alone are not enough

Pellets made for guinea pigs have vitamin C added, but the MSD Veterinary Manual explains that this vitamin breaks down with heat, light, and moisture. Food can lose much of its vitamin C within a few months. Check the date on the bag, store pellets in a cool, dark, sealed container, and always add fresh vegetables.

A sample daily menu for one adult guinea pig

• All day: a big pile of fresh timothy hay, plus fresh water
• Morning: a small handful of mixed leafy greens, such as romaine lettuce and a little parsley
• Evening: a few strips of bell pepper and a small piece of broccoli or kale
• Once a day: a small portion of plain guinea pig pellets
• A few times a week: a slice of strawberry or a small orange segment as a treat

Rotate vegetables through the week for variety. Some leafy greens, such as kale and spinach, are high in calcium or oxalates, so offer them in moderation rather than every day.

Foods to avoid

How to introduce new foods

Add one new vegetable at a time, in a small amount, and watch the droppings for a day or two. Soft or runny droppings mean you should cut back. Sudden big changes to the diet can upset the gut.

Warning signs to take to a vet

Guinea pigs hide illness. Call a vet who treats small pets if your guinea pig:

• Eats less or stops eating, even for a day
• Makes fewer or smaller droppings
• Drools, or drops food while chewing, which can mean tooth problems
• Loses weight (weigh weekly on a kitchen scale)
• Shows any signs of scurvy listed above

Like rabbits, guinea pigs can develop a slow or stopped gut. Our guide on GI stasis in rabbits explains the warning signs, many of which apply to guinea pigs too.

How to tell your guinea pig is eating well

A healthy, well fed guinea pig usually shows these signs:

• Eager at mealtimes. Many guinea pigs squeak loudly (often called "wheeking") when they hear the fridge or a bag of greens.
• Steady weight. Weigh your guinea pig once a week on a kitchen scale and write it down. A drop of more than a few percent is worth a vet call.
• Plenty of droppings. Firm, oval, and evenly sized.
• Constant hay munching. You should see the hay pile shrink every day.
• A smooth, glossy coat and bright, clear eyes.
• Normal teeth. Front teeth should be even and not overgrown. Drooling or dropping food can mean the back teeth are a problem.

Buying and storing food

Buy pellets in smaller bags so they are used within a few months, and check the date before you buy. Keep hay dry, in a breathable bag or box, away from damp floors. Wash vegetables well and serve them fresh, removing anything uneaten after a few hours so it does not spoil in the cage.

The bottom line

Unlimited hay, a daily mix of fresh vegetables rich in vitamin C, a small portion of plain guinea pig pellets, and fresh water make a healthy guinea pig diet. Vitamin C is the one nutrient you can never skip, so build every day's menu around it.