Guinea Pig Diet: Complete Feeding Guide for Healthy Cavies

By Sarah Bennett, Certified Animal Nutritionist

Getting a guinea pig's diet right is one of the most important things you can do for their long-term health. Cavies have highly specific nutritional needs that differ substantially from other small pets. Feed them correctly and they thrive for 5–8 years or more. Feed them incorrectly — even with good intentions — and you risk serious, preventable health problems including dental disease, scurvy, obesity, and digestive disorders. This guide covers everything you need to know.

The Foundation: Unlimited Timothy Hay (70% of Diet)

Hay is not a supplement or a bedding material — it is the single most important component of a guinea pig's diet, and it must be available in unlimited quantities 24 hours a day. Timothy hay is the gold standard for adult guinea pigs. It provides the long-strand fiber essential for two critical functions: proper hindgut fermentation and continuous dental wear.

Guinea pig teeth grow throughout their lives. Without sufficient hay to gnaw, the cheek teeth (molars and premolars) can become misaligned — a condition called malocclusion that causes pain, difficulty eating, weight loss, and ultimately requires veterinary intervention. There is no substitute for hay in this role. Pellets, vegetables, and fruits cannot replicate the mechanical action of long-strand grass fiber on teeth.

For young guinea pigs under six months and pregnant or nursing sows, alfalfa hay can be offered alongside or instead of timothy — it is higher in calcium and protein to support growth. For healthy adults, timothy, orchard grass, or meadow hay are preferred.

Fresh Vegetables: The Daily Fresh Food Plate (20% of Diet)

Fresh vegetables are where critical micronutrients come from, most importantly vitamin C. Guinea pigs cannot synthesize their own vitamin C and will develop scurvy without a daily dietary source. This makes fresh vegetables non-negotiable — they cannot be replaced by pellets alone.

Aim for a varied leafy green base with at least one vitamin C-rich item daily. An ideal fresh food plate might include:

• Red or green bell pepper — the richest vitamin C source per gram; a small strip daily is often sufficient to meet baseline requirements
• Romaine or green leaf lettuce — hydrating, gentle on the digestive system, readily accepted
• Cilantro (coriander) — high in vitamin C, excellent variety option
• Parsley — nutrient-dense but high in calcium; offer 2–3x per week rather than daily
• Cucumber and zucchini — hydrating, low sugar, good filler greens
• Kale and spinach — nutritious but high in oxalic acid and/or calcium; rotate, do not offer daily

Pellets: Small Amount, Vitamin C Fortified (5–8% of Diet)

Pellets serve as a concentrated nutrient supplement, not as a primary food source. A healthy adult guinea pig needs approximately 1/8 to 1/4 cup of pellets per day — not the large handfuls some owners assume are necessary. Overfeeding pellets leads to reduced hay consumption (the most common cause of dental problems) and obesity.

Choose pellets that are vitamin C-fortified and ideally plain (uniform pellet shapes rather than seed mixes). Avoid muesli-style mixes — guinea pigs selectively eat the sweet, high-sugar pieces and leave the nutritious pellets, leading to imbalanced intake. Store pellets in a cool, dry place and replace opened bags within 90 days — vitamin C degrades with time and exposure to air.

Fruit: Occasional Treat Only (2–5% of Diet)

Fruits provide vitamin C and natural sugars that most guinea pigs find irresistible, but their high sugar content means they must be firmly in the treat category. Safe fruits include apple (remove seeds and core), strawberries, blueberries, melon, kiwi, and small amounts of orange or mandarin. Offer 1–2 small pieces two to three times per week at most.

Vitamin C Every Single Day — Non-Negotiable

This bears repeating because it is the most common nutritional failure in guinea pig care. Guinea pigs need 10–30 mg of vitamin C daily (up to 50 mg when pregnant, nursing, young, or unwell). Deficiency develops within two weeks without adequate intake. Fresh vegetables — particularly bell pepper — are the most reliable source. Do not rely on water-soluble vitamin C drops, which degrade within hours in drinking water.

Water Requirements

Fresh, clean water must be available at all times. Both water bottles and heavy ceramic bowls work well — the important thing is that water is accessible and refreshed daily. Guinea pigs who eat large amounts of fresh vegetables consume some moisture through their food, but this does not replace the need for free-access water. On hot days, water intake increases significantly.

Foods That Are Never Safe for Guinea Pigs

Several common foods are genuinely dangerous for guinea pigs and must never be offered:

• Onion and garlic — contain compounds that cause hemolytic anemia (destruction of red blood cells)
• Potato — raw potato and potato sprouts contain solanine, a toxic glycoalkaloid
• Avocado — contains persin, toxic to most small mammals
• Rhubarb — high oxalic acid content, toxic in meaningful quantities
• Meat, fish, dairy, eggs — guinea pigs are strict herbivores; animal protein cannot be digested and causes serious harm
• Chocolate, caffeine, xylitol — toxic to virtually all small animals
• Iceberg lettuce in large quantities — very high water content, negligible nutrition; causes diarrhea if given as a staple
• Bread, pasta, crackers — simple carbohydrates disrupt gut flora

Feeding Schedule

Hay should be replenished continuously — check and top up at least twice daily. Fresh vegetables are best offered in the morning. Remove any uneaten fresh food after 4–6 hours to prevent it from spoiling in the cage. Pellets can be offered once daily, in the morning or evening. Remove any uneaten pellets after 24 hours. Fresh water should be changed daily and the container cleaned weekly.

Safe Food Quick Reference List

Daily greens (rotate): romaine lettuce, green leaf lettuce, red leaf lettuce, cilantro, bell pepper (all colors), cucumber, zucchini

2–3x per week: parsley, kale, dandelion greens (from pesticide-free sources), broccoli (small amounts — can cause gas), carrot (small piece), carrot tops

Occasional treats: strawberry, blueberry, apple (no seeds), melon, kiwi, orange slice