The Ultimate Guinea Pig Diet Guide: The Hay-Pellets-Veg Pyramid

Quick answer

A balanced guinea pig diet follows a strict nutritional pyramid: 80% to 85% unlimited grass hay (such as Timothy hay), 10% to 15% fresh vegetables (about 1 cup daily, focusing on leafy greens and Vitamin C-rich veggies), and 5% to 10% high-quality, uniform pellets (1 to 2 tablespoons daily). This precise balance is essential to maintain continuous dental wear, prevent life-threatening gastrointestinal stasis, and provide the daily Vitamin C that guinea pigs cannot produce on their own.

Learn the exact portions, daily schedules, and safe vegetable rotations for your

:::key-facts

• Hay is non-negotiable: Your guinea pig must have access to fresh grass hay 24/7 to keep their digestive tract moving and wear down their constantly growing teeth.
• Vitamin C is vital: Guinea pigs lack the enzyme needed to synthesize Vitamin C. They must get it daily from fresh vegetables and fortified pellets to prevent scurvy.
• Strict portion control: Limit pellets to 1-2 tablespoons per day and fresh veggies to 1 cup per day to prevent obesity and painful bladder stones.
• Avoid muesli mixes: Only feed plain, uniform grass-based pellets. Mixed foods with seeds, nuts, and colored pieces cause selective feeding and choking.
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Why it matters

To understand why your guinea pig needs a highly specific diet, you have to look at their unique evolutionary biology. Guinea pigs are hindgut fermenters. This means their digestive system relies on a complex balance of beneficial bacteria in their large intestine and cecum to break down tough cellulose. For this system to function, it requires a constant, uninterrupted flow of long-strand fiber.

Without continuous fiber, the muscles of the digestive tract slow down or stop entirely. This leads to a rapid, life-threatening condition known as gastrointestinal stasis (GI stasis). Once GI stasis sets in, harmful bacteria multiply, producing painful gas and toxins that can be fatal within 24 to 48 hours.

Beyond their digestive tract, a guinea pig's teeth are open-rooted, meaning they grow continuously throughout their entire life. If they do not spend hours every day grinding down tough, fibrous grass hay, their molars and incisors will become overgrown. This leads to painful dental malocclusion, where the teeth lock together, cut into the tongue and cheeks, and make it physically impossible for the animal to eat.

Finally, guinea pigs share a rare biological trait with humans: they cannot synthesize their own Vitamin C due to the lack of a specific enzyme (L-gulonolactone oxidase). If they do not receive adequate daily dietary Vitamin C, their bodies cannot produce collagen. This results in scurvy, a painful disease characterized by swollen joints, bleeding gums, internal hemorrhaging, and a severely compromised immune system.

:::ask-boo
Why can't guinea pigs make their own Vitamin C like other rodents?
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What good looks like

A healthy guinea pig diet is structured like a pyramid. The broad base represents the food they must eat constantly, while the narrow peak represents items that should only be given as occasional treats.

:::video{src="https://storage.googleapis.com/decennium-global.appspot.com/knowledge_assets/care_guides/hay-pellets-veg-pyramid-a-beginner-diet-plan-for-guinea-pigs/inline-backfill-1780031007385.mp4" poster="https://storage.googleapis.com/decennium-global.appspot.com/knowledge_assets/care_guides/hay-pellets-veg-pyramid-a-beginner-diet-plan-for-guinea-pigs/inline-1-1779987482029.png" alt="A visual guide showing the correct daily portions of hay, fresh vegetables, and pellets for one guinea pig."}
A visual guide showing the correct daily portions of hay, fresh vegetables, and pellets for one guinea pig.
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The ideal daily diet: 80% fresh Timothy hay, 1 cup of safe vegetables, and 1-2 tablespoons of plain pellets.

1. The Base: Unlimited Grass Hay (80-85% of the diet)

Your guinea pig should have a pile of fresh hay at least the size of their own body available at all times.

• Timothy Hay: The gold standard for adult guinea pigs. It has the ideal balance of fiber, calcium, and protein.
• Orchard Grass / Meadow Hay: Excellent alternatives or mixing options, especially if you or your pet have allergies to Timothy hay.
• Alfalfa Hay: This is not a grass hay; it is a legume. It is very high in calcium and protein. It should only be fed to growing pups (under 6 months), pregnant, or lactating mothers. Feeding alfalfa to healthy adult guinea pigs leads to excess calcium excretion, which causes painful bladder sludge and bladder stones (urolithiasis).

2. The Middle: Fresh Vegetables (10-15% of the diet)

Adult guinea pigs need exactly 1 cup of fresh, washed vegetables per day. This cup should be heavily weighted toward low-calcium leafy greens, with small portions of high-Vitamin C vegetables rotated in.

• Daily Staples: Romaine lettuce, green leaf lettuce, red leaf lettuce, cilantro, and bell peppers (any color, though red and yellow have the highest Vitamin C content).
• Occasional Additions (2-3 times a week): Kale, spinach, parsley, dandelion greens, and broccoli. These are highly nutritious but contain high levels of calcium or oxalates, which can contribute to kidney and bladder stones if fed daily.

3. The Top: Fortified Pellets (5-10% of the diet)

Pellets are a supplementary concentrate designed to guarantee your guinea pig gets their daily micronutrients, particularly stabilized Vitamin C.

• Portion: 1 to 2 tablespoons per adult guinea pig per day.
• Type: Look for plain, uniform, Timothy-grass-based pellets. Avoid any brands that include seeds, nuts, dried fruits, or colorful kibble pieces. These "muesli" mixes encourage selective feeding, where the guinea pig picks out the fatty, sugary bits and leaves the nutritious pellets behind.

4. The Peak: Treats (Less than 1% of the diet)

Fruits and root vegetables are high in sugar and can easily disrupt the delicate bacterial balance in the cecum, leading to bloating and diarrhea.

• Portion: No more than a single, thumb-sized piece of fruit or carrot 2 to 3 times a week.
• Safe Options: Apple (no seeds), blueberries, strawberries, raspberries, and small slices of carrot.

Step-by-step

Establishing a consistent daily feeding routine helps you monitor your guinea pig's appetite and ensures they always have fresh, safe food. Use this step-by-step daily schedule to keep your pet on track.

Step 1: The Morning Routine

1. Empty and Clean: Discard any leftover pellets from the day before. Wash the ceramic food bowl.
2. Measure Pellets: Place exactly 1 to 2 tablespoons of fresh, plain Timothy-based pellets into the bowl.
3. Refresh the Water: Empty the water bottle or heavy ceramic water dish. Scrub away any slippery biofilm, rinse thoroughly, and refill with fresh, cold tap or filtered water. Never add liquid Vitamin C drops to the water, as the vitamin degrades within hours when exposed to light and ruins the taste of the water, which can cause dehydration.
4. Refill the Hay: Remove any soiled, wet, or trampled hay from the floor of the cage. Stuff a generous handful of fresh, sweet-smelling Timothy hay into their hay rack or pile it in a clean area of the enclosure.

Step 2: The Afternoon Veggie Prep

1. Wash Thoroughly: Wash all vegetables under cold running water to remove pesticides, dirt, and potential parasites.
2. Measure the Portion: Aim for a total of 1 cup of mixed vegetables per guinea pig.
3. Chop Safely: Cut vegetables into manageable pieces. For stringy vegetables like celery, chop them into very small, half-inch pieces to prevent the tough fibers from wrapping around your guinea pig's teeth or tongue.
4. Serve: Place the fresh veggies in a separate shallow dish or scatter them around the cage to encourage natural foraging behavior.

:::pro-tip
To keep mealtime exciting and nutritionally balanced, use a simple weekly rotation. Pick one leafy green staple (like Romaine) for the base of the cup, add a slice of bell pepper for Vitamin C, and rotate a third "guest" vegetable (like cilantro, cucumber, or a sprig of dill) each day.
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The Weekly Veggie Rotation Planner

Use this simple rotation schedule to ensure your guinea pig gets a safe variety of nutrients without overloading on calcium:

Day	Base (Leafy Green)	Vitamin C Booster	Rotational Variety
Monday	Romaine Lettuce (3/4 cup)	Red Bell Pepper (1 slice)	Cilantro (2-3 sprigs)
Tuesday	Green Leaf Lettuce (3/4 cup)	Green Bell Pepper (1 slice)	Cucumber (2 slices)
Wednesday	Red Leaf Lettuce (3/4 cup)	Yellow Bell Pepper (1 slice)	Dill (1-2 sprigs)
Thursday	Romaine Lettuce (3/4 cup)	Orange Bell Pepper (1 slice)	Zucchini (2 slices)
Friday	Green Leaf Lettuce (3/4 cup)	Red Bell Pepper (1 slice)	Parsley (2-3 sprigs - high calcium)
Saturday	Red Leaf Lettuce (3/4 cup)	Green Bell Pepper (1 slice)	Celery (chopped, 1 tbsp)
Sunday	Romaine Lettuce (3/4 cup)	Yellow Bell Pepper (1 slice)	Small slice of Apple (Treat day!)

Step 3: The Evening Spot Check

1. Hay Top-Up: Check the hay pile. If it is running low or has been soiled, add another large handful. Guinea pigs eat constantly throughout the night, so they must never run out of hay.
2. Remove Uneaten Veggies: Take out any uneaten fresh vegetables from the afternoon to prevent mold, rot, and fruit flies.

Signs something's wrong

Because guinea pigs are prey animals, they are experts at hiding illness. A decline in appetite or a change in eating habits is often the very first sign of a serious medical issue. You must pay close attention to their waste and behavior daily.

Monitoring your guinea pig's droppings is the easiest way to assess their digestive health.

1. Changes in Droppings

• Healthy Poops: Dark brown, plump, uniform, oval-shaped, and slightly moist but firm.
• Soft Stool or Diarrhea: If the droppings are mushy, clumped together, or completely watery, this is a major warning sign. It indicates a severe disruption of the gut flora, often caused by too much sugar, sudden dietary changes, or a lack of fiber.
• Small, Tear-Shaped, or Dry Poops: This indicates dehydration or the early stages of GI stasis. The gut is slowing down, and moisture is being pulled out of the waste.
• No Poops: If you do not see any fresh droppings in the cage for 6 to 12 hours, this is a critical emergency.

2. Physical and Behavioral Red Flags

• Anorexia: Refusing to eat pellets, veggies, or hay. A guinea pig that stops eating will rapidly develop GI stasis.
• Slobbers (Drooling): If the fur under your guinea pig's chin or chest is wet, or if they drop food out of their mouth while trying to chew, they likely have overgrown molars or dental malocclusion.
• Hunched Posture and Puffed Fur: This is a universal sign of pain in guinea pigs. They will sit in a corner, look miserable, and refuse to move.
• Lethargy: Not running to the cage side for food or showing no interest in fresh veggies.
• Crusty Eyes or Nose, and Swollen Joints: These are classic symptoms of scurvy (Vitamin C deficiency). You may also notice they squeak in pain when touched or move with a stiff, hopping gait.

:::warning
If your guinea pig has not eaten anything or has not passed any droppings for 12 hours, they are in active gastrointestinal stasis. This is a life-threatening emergency. Go to an exotic animal emergency vet immediately.
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When to call your vet

Guinea pigs have a incredibly fragile metabolism. What looks like a minor off-day can become fatal within 24 hours. You should contact an exotic animal veterinarian immediately if you notice any of the following:

• Complete loss of appetite: Your guinea pig refuses all food, including their favorite treats, for more than 6 to 8 hours.
• Watery diarrhea: Liquid or foul-smelling stool can cause fatal dehydration and toxic shock within hours.
• Signs of dental pain: Drooling, grinding teeth loudly, chewing on one side of the mouth, or showing interest in food but refusing to bite into it.
• Blood in the urine: If you notice pink or red stains on their bedding, or if your guinea pig squeaks or strains while urinating, they may have painful bladder stones or a urinary tract infection.
• Severe lethargy: Your pet is unresponsive, cold to the touch, or unable to stand.

:::ask-boo
What are the first signs of GI stasis in guinea pigs, and what should I do while waiting for the vet?
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Common mistakes

Even well-meaning owners can make critical errors when setting up their guinea pig's diet. Avoiding these common pitfalls will save your pet from unnecessary pain and expensive veterinary bills.

1. Feeding Alfalfa Hay to Adult Guinea Pigs

Alfalfa is sweet and tasty, so guinea pigs love it. However, its high calcium content is incredibly dangerous for adults. Guinea pigs absorb calcium in proportion to what they eat, and any excess is excreted through their kidneys into their bladder. This leads to "bladder sludge" (thick, gritty urine) and solid calcium oxalate bladder stones. These stones cannot be dissolved with medication and almost always require invasive, risky surgery to remove.

2. Using Vitamin C Water Drops

Many pet stores sell liquid Vitamin C drops to put in your guinea pig's water bottle. This is highly ineffective. Vitamin C is extremely unstable and degrades rapidly when exposed to light, air, and water; within 8 to 12 hours, virtually no active vitamin remains. Furthermore, these drops often give the water a bitter, chemical taste. This can cause your guinea pig to stop drinking, leading to severe dehydration.

Avoid muesli mixes with seeds and colorful pieces; they cause selective feeding and are choking hazards.

3. Buying Muesli-Style Food Mixes

Commercial food mixes containing seeds, nuts, dried fruits, and colorful dyed kibble are marketed as premium diets, but they are highly dangerous. Seeds and nuts are choking hazards and are far too high in fat for a guinea pig's low-fat digestive system. Additionally, guinea pigs will selectively eat the sweet, fatty pieces and ignore the healthy grass pellets, leading to severe nutritional deficiencies, obesity, and dental disease.

4. Introducing New Foods Too Quickly

A guinea pig's gut microbiome is highly specialized. If you suddenly introduce a large amount of a new food—such as giving them a massive bowl of fresh grass or a pile of kale for the first time—the bacteria in their cecum cannot adapt quickly enough. This causes rapid fermentation, painful gas, bloating, and severe diarrhea. Always introduce any new vegetable slowly, starting with a tiny, postage-stamp-sized piece and gradually increasing the portion over a week.

Quick FAQs

Can guinea pigs eat grass from the lawn?

Yes, fresh grass is highly nutritious and mimics their natural wild diet. However, you must ensure the grass has not been treated with any chemical fertilizers, pesticides, or weed killers. It should also not be harvested from areas where wild rabbits, dogs, or cats defecate, as this can transmit parasites. Introduce fresh grass to their diet very slowly to prevent bloating.

How do I get my guinea pig to eat more hay?

If your guinea pig is ignoring their hay, try switching to a different cut or brand. Second-cut Timothy hay is usually the most popular because it is leafy and sweet. You can also try Orchard grass or Meadow hay for a different texture. Make hay fun by stuffing it inside cardboard toilet paper rolls, mixing in safe dried herbs like marigold or chamomile, and ensuring the hay is always kept clean, dry, and off the cage floor.

Can guinea pigs eat celery?

Yes, guinea pigs can eat celery, but it must be prepared carefully. Celery contains long, tough, fibrous strings that can easily wrap around a guinea pig's teeth or get lodged in their throat. Always chop celery into very small, quarter-inch pieces before feeding it to them, and limit it to an occasional treat due to its high water content.

Is Timothy hay the only safe hay for adult guinea pigs?

No, Timothy hay is simply the most common and widely available. Orchard grass, Meadow hay, Bluegrass, and Brome hay are all excellent, safe, low-calcium grass hays that can be fed unlimitedly to adult guinea pigs. Mixing different types of grass hay is actually highly recommended to provide a variety of textures and nutrients.