“What do I actually feed this thing?” — it’s the first question every new guinea pig owner asks me, and I get it. Pet stores are full of brightly colored bags promising “gourmet guinea pig food” with dried corn, yogurt drops, and seed mixes. Let me save you some money and some vet bills: almost none of that belongs near your guinea pig. As an exotic veterinary assistant who feeds four very opinionated guinea pigs every day, here’s what actually works.

The Guinea Pig Diet at a Glance

A guinea pig diet is way simpler than the pet industry wants you to believe:

80% unlimited timothy hay — always available, never restricted
Guinea pig pellets — vitamin C fortified, plain (no colorful bits)
1 cup fresh vegetables per pig per day
Fresh water always available
NO sugary treats marketed for guinea pigs — yogurt drops, seed sticks, and treat mixes are all junk food

If you get the hay right, you’re already most of the way there. Everything else is fine-tuning.

Hay: The Foundation (80% of Diet)

Timothy hay is the single most important food in your guinea pig’s life. It should be available 24/7, unlimited. I refill my pigs’ hay racks multiple times a day, and they demolish it. Luca treats his hay rack like an all-you-can-eat buffet — the second I top it off, he’s face-first in it.

Luca Luca, mid-snack. This is his default state.

Hay does two critical things. First, guinea pig digestive systems need constant fiber to keep moving. A pig that stops eating hay is headed for GI stasis — a life-threatening shutdown of the gut. I’ve seen it at the clinic, and it is scary. Second, guinea pig teeth never stop growing. The grinding motion from chewing hay files them down naturally. Without enough hay, teeth overgrow and develop painful spurs that make eating impossible.

Choosing the right cut: Second-cut timothy hay is softer and leafier — great for picky eaters (looking at you, Coco). First-cut has thicker stems and more fiber, which is better for dental wear. I offer both and let them sort it out.

Orchard grass is a good supplement for pigs who turn their nose up at timothy. It’s slightly sweeter and softer, and Kai seems to prefer it on his more discerning days.

A note on alfalfa: Alfalfa hay is higher in calcium and calories. It’s appropriate for baby guinea pigs under 6 months and pregnant or nursing sows, but it should not be fed to healthy adults — excess calcium can contribute to bladder stones.

For high-quality hay delivered to your door, I recommend Small Pet Select on our small mammal resources page.

Pellets: Choose Wisely

Pellets are a supplement, not a main course — even though my pigs act like pellets are the main event. Each guinea pig needs about 1/8 cup per day, and that’s it. Overfeeding pellets is one of the most common mistakes I see, and trust me, your pigs will try to convince you they’re starving.

Choose plain, timothy-based pellets with no added seeds, dried fruit, or colorful bits. My go-to brands are Oxbow Essentials Adult Guinea Pig Food and KMS Hayloft pellets. Those muesli-style mixes you see at pet stores — the ones that look like trail mix — are a problem. Guinea pigs will pick out the sugary, fatty pieces and leave the nutritious parts behind. It’s the equivalent of letting a toddler eat only the marshmallows from a cereal box.

Pellets should be fortified with vitamin C, but vitamin C degrades over time. Buy small bags and use them within a few months of opening. Check the manufacturing or best-by date.

Fresh Vegetables: Daily Essentials

This is where my pigs’ personalities really come out. Every guinea pig should get approximately 1 cup of fresh vegetables per day, offered as a mix of high-vitamin-C options and staple greens.

Milo the guinea pig Milo hears the vegetable drawer open from two rooms away. Every. Single. Time.

Milo is obsessed with vegetables in a way that borders on unreasonable. The fridge door opens, the wheeking starts — full volume, no shame. He’d eat bell peppers for every meal if I let him. Luca is right behind him, ready to steal whatever Milo drops. Coco, meanwhile, sniffs everything suspiciously and sometimes decides that today he doesn’t like cilantro, even though he devoured it yesterday.

High Vitamin C (feed daily)

Bell peppers — red, yellow, and orange varieties have the highest vitamin C content of any common vegetable. A single slice of red bell pepper delivers more vitamin C than most supplements. This is the single best vegetable you can feed, and it’s Milo’s reason for living.
Parsley and cilantro — excellent vitamin C sources and most pigs love them
Kale — high in vitamin C but also high in calcium, so feed in moderation

Staple Greens (daily rotation)

Romaine lettuce — a reliable daily green (never iceberg — it has virtually no nutritional value and can cause digestive upset)
Green leaf lettuce — gentle on the stomach, good for daily feeding
Endive and escarole — nutritious options to keep the rotation interesting

Occasional Treats (2-3 times per week)

Cucumber and zucchini — hydrating but low in nutrition
Carrot — small amounts only, as carrots are high in sugar
Blueberries and strawberries — tiny pieces as a rare treat (Luca will sell his soul for a blueberry, but he gets maybe two a week)

Foods to AVOID

This is the non-negotiable list. Some common foods are dangerous or straight-up toxic to guinea pigs:

Iceberg lettuce — causes bloating and diarrhea
Potatoes — toxic to guinea pigs
Onions and garlic — toxic
Avocado — toxic
Chocolate, dairy, bread, pasta — guinea pigs are strict herbivores
Any processed human food — if it came from a box or a bag with a barcode, it’s not guinea pig food

When in doubt, don’t feed it. Stick with the safe list above and your pigs will be just fine.

Vitamin C: The Critical Nutrient

Guinea pigs cannot produce their own vitamin C. They’re one of the only mammals that share this trait with humans. Without enough vitamin C, they develop scurvy — and it happens faster than you’d think. I’ve seen it at the clinic, and it’s heartbreaking because it’s entirely preventable.

Signs of vitamin C deficiency include:

Lethargy and reluctance to move
Swollen, painful joints
Rough, poor-quality coat
Hind leg weakness or an unusual gait
Slow wound healing

Daily requirements:

Healthy adults: 25-30mg per day
Pregnant or nursing sows: 50mg per day

The best sources are fresh bell peppers and a varied vegetable rotation, supported by vitamin C-fortified pellets. If your pig is a picky eater or recovering from illness, you can supplement directly with Oxbow Natural Science Vitamin C tablets.

Do NOT add vitamin C drops to their water. Vitamin C degrades rapidly in water (especially in light), so your pig gets almost none of it. Worse, it changes the taste of the water, and some guinea pigs will drink less as a result — creating a dehydration risk on top of the deficiency. It’s a lose-lose.

Water

Fresh water should be available at all times via a water bottle — not a bowl. Bowls get contaminated with bedding, hay, and droppings within minutes (ask me how I know). Guinea pigs typically drink 80-100ml per day, though this varies with temperature and vegetable intake.

Clean the water bottle thoroughly at least once a week, and check the sipper tip daily to make sure it’s dispensing properly. A stuck sipper is a silent emergency — your pig can’t tell you the water isn’t coming out.

Feeding Schedule

My pigs thrive on routine, and yours will too. Here’s what our daily schedule looks like:

Hay: Always available — I replenish throughout the day as needed
Pellets: Once daily, in the morning (cue the collective meltdown of excitement)
Vegetables: Twice daily — morning veggie service and an evening round
Cleanup: I remove uneaten fresh vegetables after a few hours to prevent spoilage

Getting the Diet Right Makes Everything Easier

A proper diet prevents the vast majority of health problems I see in guinea pigs. Dental disease, GI stasis, scurvy, obesity, bladder stones — they all trace back to nutrition. Unlimited hay, measured pellets, a daily cup of varied vegetables, and fresh water. That’s the foundation for a long, healthy life.

For more on guinea pig health, read our complete guinea pig care guide and learn to recognize the signs your guinea pig needs a vet. You’ll find our recommended hay, pellet, and supply brands on the small mammal resources page, and if you’re in the San Francisco Bay Area, check out our exotic pet care services.

Guinea Pig Diet & Nutrition