Guinea pig nutrition guide: hay, vitamin C, pellets, and common mistakes
The guinea pig is the pet whose primary preventable cause of death is vitamin C deficiency. Not an infectious disease, not an accident, not a genetic predisposition: a simple nutritional shortfall in a vitamin found in any seasonal vegetable. And yet scurvy - the vitamin C deficiency disease - is still frequently observed in veterinary practice in guinea pigs whose owners believed they were feeding them correctly.
This guide covers everything: the unusual biology of the guinea pig and its inability to synthesise vitamin C, the diet fundamentals (hay, pellets, vegetables), foods to absolutely avoid, the most common mistakes, and a selection of the best brands rated on PetFoodRate. The French version of this guide is available at /fr/blog/fr-alimentation-cochon-inde-guide/. For our complete product selection, see our best guinea pig food page.
Biology: why the guinea pig is unique
The inability to synthesise vitamin C
The vast majority of mammals synthesise their own vitamin C from glucose in the liver. Guinea pigs, like humans and other primates, cannot. This mutation occurred during the evolution of the South American Caviinae: they lost the gene coding for L-gulonolactone oxidase (GULO), the enzyme that catalyses the final step of ascorbic acid biosynthesis.
In practice, this means the guinea pig is entirely dependent on dietary intake to meet its vitamin C needs. Those needs are significant: between 10 and 30 mg per kilogram of body weight per day for a healthy animal, and up to 30 to 50 mg/kg/day for a pregnant female or a convalescing animal.
An adult guinea pig weighing 1 kg needs a minimum of 10 to 30 mg of vitamin C every day, without interruption. If these intakes are not met, the first signs of scurvy appear within 2 to 3 weeks.
What vitamin C does in the body
Vitamin C (ascorbic acid) is essential for collagen synthesis, the structural protein of all connective tissues: bones, cartilage, gums, blood vessels, skin. Without vitamin C, existing collagen degrades and new collagen cannot be synthesised.
Clinical signs of scurvy in guinea pigs progress rapidly:
- Lethargy, loss of appetite, dull coat
- Muscle stiffness, lameness (intramuscular haemorrhages)
- Swollen and bleeding gums, fragile teeth
- Painful and swollen joints (haemarthroses)
- Internal haemorrhages, death
This progression can unfold over 4 to 6 weeks from a vitamin C-free diet. Treatment is effective if started early: injectable or oral vitamin C at therapeutic doses (50-100 mg/kg/day for 1-2 weeks). Beyond a certain point, bone and joint lesions may be irreversible.
The guinea pig food pyramid
The ideal guinea pig diet rests on three pillars, in order of importance.
Pillar 1: hay (80 pourcent of dietary volume)
Hay is the essential and irreplaceable foundation of the guinea pig's diet. It must be available ad libitum, 24 hours a day, 7 days a week. It cannot be rationed.
Why is it so important?
Dental wear. Guinea pig teeth are hypsodont (continuously growing). They never stop growing. Chewing hay - a prolonged, repetitive lateral movement - wears teeth evenly and prevents malocclusion (teeth that do not wear correctly, grow misaligned, and eventually prevent the animal from eating). Dental malocclusion is one of the leading causes of digestive problems and death in adult guinea pigs.
Gut motility. Guinea pigs are herbivores whose digestive system is designed to process large volumes of fibrous plant material continuously. A diet low in long fibre slows transit, promotes gastrointestinal stasis and bloating, and can lead to digestive obstruction. GI stasis is potentially fatal.
Natural satiety and obesity prevention. Hay is low in calories and very bulky. A guinea pig with hay available ad libitum eats fewer pellets and sugary vegetables, which prevents obesity.
Which hay to choose?
| Hay type | Nutritional profile | Recommended for |
|---|---|---|
| Timothy grass | High fibre, moderate protein, moderate calcium | Adults - standard reference |
| Orchard grass | Similar to timothy, softer texture | Adults, guinea pigs with sensitive teeth |
| Meadow hay | Diverse plant species, variable | Adults as a complement |
| Alfalfa (lucerne) | High protein, high calcium | Juveniles (<6 months), pregnant females only |
| Wheat or barley hay | Adequate fibre | Complement, less data available |
Alfalfa is not suitable for healthy adult guinea pigs. Its high calcium content can promote urinary stones; its protein richness is inappropriate for a sedentary adult. Reserve it for young animals under 6 months and pregnant or lactating females.
Oxbow Western Timothy Hay is our absolute reference: quality-controlled timothy hay, long cut, no dyes or additives. Science Selective offers excellent diversified meadow hay. Both earn an A rating on our guinea pig food page.
Pillar 2: vitamin C pellets (15 pourcent)
Pellets do not replace hay but provide a concentrated source of essential nutrients, particularly vitamin C. They must be chosen carefully.
What a good pellet must contain:
- Timothy hay as first ingredient
- Added and titrated vitamin C (sodium or calcium ascorbate, more stable than pure ascorbic acid)
- No artificial colorants, no added sugars, no colourful dried fruit pieces
- No sunflower or pumpkin seeds (too fatty)
- Crude protein: 14-18 pourcent (dry matter)
- Crude fibre: minimum 15-20 pourcent
Critical note: vitamin C is unstable. It degrades under light, heat and moisture. Pellets enriched with vitamin C have a limited stability window. A bag opened for more than 90 days may have lost a large portion of its declared vitamin C content. Fresh vegetables remain the most reliable and stable source of vitamin C.
Top guinea pig pellet brands compared
| Brand | PetFoodRate score | First ingredient | Vitamin C | Price (kg) |
|---|---|---|---|---|
| Oxbow Essentials Adult Guinea Pig | A (91/100) | Timothy hay | Yes, titrated | 9.50 euros |
| Science Selective Guinea Pig | A (89/100) | Timothy grass | Yes, titrated | 8.20 euros |
| Burgess Excel Guinea Pig | A- (86/100) | Dried grass, timothy hay | Yes | 7.50 euros |
| Supreme Tiny Friends Farm Gerty | B+ (80/100) | Wheat flour, grass | Yes | 6.80 euros |
| Versele-Laga Complete | B (76/100) | Grains, grass | Yes | 5.90 euros |
| Generic colourful muesli mix | D (42/100) | Corn, grains, coloured elements | No or unstable | 3.50 euros |
Colourful "muesli" mixes (with dried fruit pieces, seeds, grain fragments) must be avoided. They induce selective picking behaviour (the guinea pig eats the sweet elements and ignores the nutritious pellets) which leads to nutritional deficits even if the overall stated composition appears "complete."
Pillar 3: fresh vegetables (15-20 pourcent)
Fresh vegetables are the most reliable and bioavailable source of vitamin C for guinea pigs. They must be given daily, in sufficient quantity to cover vitamin C needs independently of pellets.
The 3-5 vegetable rule per day: rotate vegetables daily to provide micronutrient diversity and prevent dietary boredom.
Best vitamin C sources for guinea pigs
| Vegetable | Vitamin C (mg/100g fresh) | Recommended portion | Notes |
|---|---|---|---|
| Red bell pepper | 128 mg | 1-2 rings / day | Best source, very popular with guinea pigs |
| Green bell pepper | 80 mg | 1-2 rings / day | Slightly less rich |
| Fresh parsley | 133 mg | A few sprigs / day | Rich but limit (oxalic acid) |
| Kale | 93 mg | 1-2 leaves / day | High calcium, alternate with other greens |
| Broccoli | 89 mg | 1-2 florets / day | Well tolerated |
| Brussels sprouts | 85 mg | 1-2 / day | Gas if excess |
| Fresh spinach | 28 mg | 1-2 leaves / week | Oxalates, limit |
| Romaine lettuce | 8 mg | 1 leaf / day | Complement only, not base |
Red bell pepper is the best practical source of vitamin C for guinea pigs. A slice of red pepper (around 20-25g) delivers approximately 25-30 mg of vitamin C, already covering a significant portion of daily needs. It is typically very well accepted by guinea pigs, affordable, available year-round, and has an overall favourable nutritional profile (fibre, low sugar compared to fruits).
Other beneficial vegetables (lower in vitamin C but nutritious)
| Vegetable | Nutritional value | Frequency |
|---|---|---|
| Carrot | Beta-carotene, fibre | 2-3x/week (sugars, moderate) |
| Cucumber | Hydration, light fibre | Daily in summer |
| Courgette | Fibre, low calorie | 3-4x/week |
| Fennel | Vitamins C and B, digestive | 2-3x/week |
| Celery | Fibre, hydration | 2-3x/week |
| Sweet potato | Beta-carotene, vitamin C | 1-2x/week |
| Endive | Fibre, vitamins | 3-4x/week |
Toxic and dangerous foods
Absolutely forbidden
Avocado: persin toxic to small mammals - cardiac risk.
Chocolate, coffee, tea: cardiotoxic methylxanthines.
Onions, garlic, leeks, chives: thiosulphates cause haemolysis - destruction of red blood cells.
Rhubarb: extremely high oxalic acid - nephrotoxic.
Raw or green potato: solanine toxic (cooked potato without green parts is less concerning but nutritionally useless).
Green tomatoes and tomato leaves: solanine (ripe red fruit is acceptable in small amounts).
Fruit pits: potential cyanide.
Common ornamental plants: fern, ivy, philodendron, begonia, geranium, lily of the valley, tulip, daffodil - many are toxic.
To avoid or strongly limit
Iceberg lettuce: almost pure water, no nutritional value, can cause watery diarrhoea and electrolyte dilution.
Excess spinach and beetroot: oxalic acid chelates calcium and may promote urinary stone formation.
Excess brassicas (broccoli, cabbage, cauliflower, Brussels sprouts): intestinal gas if given in large amounts or too frequently.
Sugary fruits (grapes, bananas, cherries, figs): high fructose disrupts intestinal flora and promotes obesity. Fruits can be given occasionally (1-2 times per week, small portion) as a treat, never as a dietary base.
Seeds, nuts, sunflower seeds: too high in fat, unsuitable for the herbivore guinea pig's metabolism.
Water: an often underestimated aspect
Guinea pigs must have access to fresh water at all times. The amount consumed varies with fresh vegetable intake (a diet rich in watery vegetables reduces free water needs) but access must be permanent.
Water bottle or bowl? Both work. The ball-tipped water bottle is more hygienic (less contamination by droppings and vegetable debris) but some guinea pigs prefer to drink from a flat bowl. The key is to change the water daily in either case.
Never add vitamin C to water. Ascorbic acid degrades within hours in open water exposed to light. Guinea pigs frequently urinate into their water bottles (calcium deposits). Vitamin C added to water does not ensure a reliable dose and can encourage bacterial growth in the bottle. Vitamin C must come through fresh vegetables and enriched pellets.
Caecotrophy: understand it, do not panic
Guinea pigs, like rabbits, practice caecotrophy: they directly ingest certain of their own droppings (caecotropes or "soft faeces") produced at night. This behaviour is normal and essential - it allows double fermentation of food and the assimilation of vitamins B12, B6, K and microbial proteins that would not otherwise be absorbed.
An owner who notices their guinea pig "eating its droppings" should not be alarmed and certainly should not frantically clean the cage to prevent it. Caecotropes are soft, clustered, slightly glossy faeces - distinct from the round, dry pellets that are not reingested.
Weight monitoring: a key indicator of diet quality
Guinea pigs hide illness well - it is a prey animal survival instinct. Regular weight monitoring is the most practical way to detect a nutritional or health problem before it becomes serious.
How to monitor weight:
- Use a kitchen scale accurate to 1g
- Weigh your guinea pig at the same time each week (morning, before first feeding)
- Record the weight in a notebook or app
- Normal adult weight range: 700-1200g (males tend to be larger than females)
- A loss of more than 50g in one week, or more than 100g over a month, warrants a veterinary consultation
Weight trends and what they indicate:
| Trend | Possible cause | Action |
|---|---|---|
| Gradual weight gain over months | Excess pellets, too much fruit, insufficient exercise | Reduce pellets, increase hay, check living space |
| Gradual weight loss | Dental malocclusion, vitamin C deficiency, parasites, chronic illness | Veterinary consultation |
| Rapid weight loss (>50g/week) | Acute illness, pain, dental pain preventing eating | Urgent veterinary consultation |
| Stable weight, normal activity | Good dietary balance | Continue current regime |
A healthy adult guinea pig's weight fluctuates within a narrow range day to day. Wide daily swings (more than 30-40g between mornings) can indicate irregular food access, digestive instability, or a behaviour problem (a dominant cage mate blocking food access in a group setting).
Hay quality: what to look for
Not all hay is equal and the quality varies considerably between brands and batches. Poor quality hay - dusty, brown, mouldy, highly compacted - can cause respiratory problems and may be refused by the guinea pig altogether.
Signs of good quality hay:
- Green to pale gold colour (not brown or grey)
- Fragrant, slightly sweet smell (not musty or chemical)
- Long fibre strands visible
- Low dust when handled
- No visible mould patches or discolouration clusters
Signs of poor quality hay to avoid:
- Musty or fermented smell
- Grey or brown colour throughout
- Excessive dust (respiratory irritant)
- Clumped and compressed beyond normal baling
- Any visible mould (white, green or black patches)
Store hay in a breathable bag (not plastic), in a cool dry place away from direct sunlight. Vacuum-packed hay shipped in sealed bags is typically fresher than hay sold in open bins at pet shops where it may have been exposed to ambient moisture for weeks.
Hay and bedding: Do not use hay as bedding. Hay soiled with urine and droppings loses its nutritional value and can harbour bacteria and fungi. Use a separate bedding material (paper-based, wood shavings) and keep fresh hay in a dedicated rack or holder.
The 7 most common feeding mistakes
1. Rationing hay or only changing it every 3 days. Hay must be available 24 hours a day without restriction. Slightly damp or soiled hay must be removed and replaced immediately - do not wait for it to be fully consumed.
2. Assuming pellets are sufficient for vitamin C. Pellets are a source of vitamin C but a degradable one. Daily fresh vegetables are indispensable.
3. Giving a colourful muesli mix instead of uniform extruded pellets. Selective picking is the direct consequence. The guinea pig eats the sweet parts and leaves the nutritious ones.
4. Giving too much fruit. A guinea pig should not eat fruit every day. Strawberries, grapes, apples, pears, blueberries are occasional treats (1-2 times per week, a small amount), not dietary staples.
5. Not varying vegetables. A monotonous diet of only lettuce and carrot does not cover vitamin C or micronutrient needs. Vegetable diversity is as important as quantity.
6. Ignoring warning signs. A guinea pig that eats less, limps, has swollen gums or a dull coat may be showing vitamin C deficiency. A prompt veterinary assessment is essential - scurvy treated early resolves well.
7. Cohousing with different rodents. Guinea pig nutritional needs are incompatible with those of hamsters or gerbils. A guinea pig sharing a cage with a hamster may access inappropriate foods (fatty seeds, animal proteins). Species must be kept separately. For species-specific nutrition, see also our hamster nutrition guide.
Our full selection
For the complete list of guinea pig foods, hay and pellets we have rated, with ingredient analyses and A-E grades, visit our dedicated page: best guinea pig food.
Also explore:
- Our methodology page to understand our evaluation criteria
- Our overall rankings for the best brands across all species
- Our rabbit nutrition guide for another hay-dependent herbivore
- Our how to read a pet food label guide for understanding ingredient lists
- Our bird nutrition guide for vitamin A and D3 in a different species
Sources
- Navia JM, Hunt CE. Nutrition, nutritional diseases, and nutrition research applications. In: Wagner JE, Manning PJ (eds). The Biology of the Guinea Pig. Academic Press, 1976: 235-267.
- Zafra MA, et al. Scurvy in guinea pigs (Cavia porcellus). Journal of Exotic Pet Medicine, 2013; 22(2): 183-189.
- Hrapkiewicz K, Medina L. Clinical Laboratory Animal Medicine: An Introduction. 3rd edition. Blackwell Publishing, 2007. Chapter 5: Guinea pigs.
- Quesenberry KE, Carpenter JW. Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery. 3rd edition. Saunders Elsevier, 2012. Chapter 19: Guinea pigs, pp. 279-294.
- Clauss M, et al. The importance of fibre in the diet of lagomorphs and hystricomorph rodents. Proceedings of the Nutrition Society, 2010; 69(2): 244-255.
- Oxbow Animal Health. Guinea pig care guide: nutrition fundamentals. 2022. https://www.oxbowanimalhealth.com/care-guides/guinea-pig
- Sophie Lefevre, Species Nutrition Specialist, PetFoodRate