What do guinea pigs eat? A vet-approved guide to hay, pellets, vegetables, and vitamin C supplementation.
Guinea pigs, like humans, cannot synthesize their own Vitamin C. This makes them one of the few mammals that can develop scurvy — a potentially fatal condition caused by Vitamin C deficiency. Every aspect of their diet should account for this critical need.
Daily Vitamin C requirement: 10-30 mg per day for healthy adults, up to 50 mg for pregnant, nursing, or ill guinea pigs.
Hay is the cornerstone of guinea pig nutrition. It provides fiber for healthy digestion, wears down continuously growing teeth, and should be available 24/7 in unlimited quantities.
Best hay: Timothy hay is the gold standard. Kaytee Timothy Hay and Oxbow Timothy Hay are our top picks for consistency and quality. Both are sun-dried, hand-selected, and available in bulk.
Hay types to know:
Timothy hay: Primary hay for adults. High fiber, low protein, low calcium.
Orchard grass: Good alternative/supplement. Similar nutritional profile, sweeter taste.
Alfalfa hay: HIGH in calcium. Only for babies (under 6 months) and pregnant/nursing sows. DO NOT feed to adult guinea pigs — causes bladder stones.
Pellets supplement hay with concentrated vitamins and minerals. But they're a supplement, not a main course.
Best pellets: Oxbow Essentials Guinea Pig Food
Uniform pellets (no colored pieces, seeds, or dried fruit that allow selective eating), Timothy hay-based, fortified with stabilized Vitamin C. This is a widely vet-stocked guinea pig pellet.
Pellet rules:
1/8 cup per guinea pig per day (not unlimited!)
Plain pellets only — no muesli-style mixes
Fresh vegetables provide essential Vitamin C, variety, and enrichment. Serve approximately 1 cup of mixed vegetables per guinea pig daily.
High Vitamin C vegetables (daily staples):
Bell peppers (red/yellow/orange — highest Vitamin C of any vegetable!)
Cilantro
Parsley (in moderation — high calcium)
Tomatoes (fruit only, not leaves/stems — those are toxic)
Guinea pigs need constant access to clean water. Use a water bottle or a heavy ceramic bowl (bottles are cleaner, bowls are more natural).
Important: Add Vitamin C drops to water? NO — Vitamin C degrades rapidly in water, tastes bad (guinea pigs drink less), and creates bacterial growth. Get Vitamin C from vegetables and pellets instead.
Never feed:
Potatoes (solanine is toxic)
Onions and garlic (damage red blood cells)
Avocado (persin is toxic)
Chocolate (theobromine is toxic)
Iceberg lettuce (no nutrition, causes diarrhea)
If your guinea pig isn't getting enough Vitamin C from vegetables, supplementation may be necessary:
Best method: Oxbow Natural Science Vitamin C tablets (66 mg each). Most guinea pigs eat them as treats. Break in half for daily dosing.
Signs of Vitamin C deficiency (scurvy):
Rough, dull coat
Swollen, painful joints
Reluctance to move
Morning: Fresh vegetables (1 cup), fresh pellets (1/8 cup), check hay supply
Evening: Top off hay, check water bottle, remove any uneaten vegetables (they spoil)
Always available: Timothy hay, clean water
1. Too many pellets — Leads to obesity and selective eating. 1/8 cup per pig, period.
2. Muesli-style food — Guinea pigs pick out sugary pieces and leave the nutritious ones
3. Not enough hay — If your guinea pig has an empty hay rack, something is wrong
4. Alfalfa hay for adults — Too much calcium causes bladder stones
5. Vitamin C drops in water — Ineffective and makes water taste bad
6. Too much fruit — Sugar causes obesity and dental problems
Timothy hay, bought in bulk — the single biggest item by volume
Pellets — a 5 lb bag covers roughly a month for two pigs
Fresh vegetables daily — the biggest recurring cost after hay
Expect hay and fresh produce to account for most of the monthly spend on a pair
Guinea pig nutrition boils down to four things: unlimited timothy hay, measured pellets, daily fresh vegetables rich in Vitamin C, and clean water. Get these right and you'll have a healthy, happy guinea pig for 5-8 years. Skimp on any of them and you risk serious health problems. When in doubt, more hay is always the answer.