Celia Haddon - Cat Expert

Understanding animals through their behaviour


pig in hay

Guinea pigs have a digestive system that relies on some food being digested twice – diagram here.  Most of their digestion takes place not in the stomach but in the cecum lower down the gut. They produce two types of droppings. One type, which is rich in nitrogen, they eat, usually at night, as a way of getting extra nourishment (Merck Veterinary Manual, 2013).

They need lots of fibre and fresh vegetables or grass because they lack an enzyme which can convert food to vitamin C (Lee 2010). If they don’t have enough fibre in their diet, the passage of food through their gut slows down or stops altogether, which is a veterinary emergency (McBride 2011). Or they may start chewing each other’s hair, which is called barbering (White, 2013). They have sensitive digestions so introduce new food a little at a time and make sure all fruit and veg is washed.

So their main diet (80% to 90%) must be sweet dry hay and grass, (never grass cuttings). Good hay should be always available. Buy meadow hay or Timothy hay from West Willows or from Petlife or Burgess or Dust Free Hay. Fresh green vegetables such as spring greens, broccoli, kale, cabbage, cauliflower leaves, dandelion, green peppers, vetch, clover, chickweed, watercress, shepherd’s purse, plantain, and groundsel. Root veg like carrot, parsnip, swede, beetroot, are fattening so feed sparingly. Feed fruit like apple and pear only in very tiny quantities as a treat.

Only 5% of their diet should be dry guinea pig food. Do not feed muesli diets. Some guinea pigs pick out the richest bit of a mix and will not eat the rest up. So feed pellets (nuggets), rather than mix, choosing those with the least protein and most fibre. As a rough guide an egg cupful of pellets is about the right amount for one guinea pig (McBride 2011). Don’t buy huge amounts as a time, as it is very important to use them all up before the “Best before” date – the vitamin C degrades if they are kept too long (Wolfensohn & Lloyd, 2003)

Burgess Excel and Essential Cavy Cuisine (scroll right down website) are good pellet foods but should only be a small part of their diet. If you find it difficult to find green food for them in the winter, add some Vitamin C. Putting vitamin C in the water doesn’t work well: instead buy special tablets here. Follow instructions. Too much vitamin C in tablet form is bad for them (Orcutt 2005). Guinea pigs form strong food preferences and prefer a diet they are used to, so if you need to change their diet do it slowly over several weeks, gradually adding more of the new food (Lee 2010).

Clean fresh water from a feeding bottle or a bowl must be always available. Guinea pigs tend to shove bits of food up their feeding bottles, so these must be inspected and cleaned daily. They are naturally messy animals!

Never feed them rabbit food – it doesn’t have enough vitamin C in it and sometimes it contains additives which are bad for guinea pigs.  If you must keep a rabbit and a guinea pig together (not recommended at all) then feed guinea pig food which will not harm the rabbit.


Onions, leek, garlic, rhubarb, potatoes and rhubarb are potentially poisonous (McBride 2011). Chocolate may be fatal. Human foods such as white bread and biscuits are bad for them. Sticky treats sold in pet shops are fattening as is corn or grain. Never feed anything sold loose in large sacks – it may be of poor quality and contaminated with fungus etc. Lettuce should only be fed as an occasional treat. Citrus fruit can cause mouth sores from acidity. Alfalfa hay (as opposed to Timothy or meadow hay) is too rich and may cause bladder stones (Hoeffer 2006).


Chewing and gnawing is essential to keep their teeth healthy (Reinhardt 2002). As well as sweet hay, they will benefit from chewing on branches of apple, pear, willow or hazel. Also elm, maple and birch (Knegt 2012). You can usually find willow or hazel in hedges. Make sure you know what branches you are picking. Be careful to wash them, and scrape off any lichen, before giving them to your guinea pig. Do not use branches from any tree which has fruit with stones. Do not give evergreen or coniferous or any tree branch which might be poisonous. Willow toys sold for rabbits are fun for them to chew – www.westwaleswillows.co.uk


Do not feed sticky treats or human food.  Feed fresh root veg like carrots but not too much of them. Or feed tiny little bits of apple or pear. Or feed Burgess nature snacks.


De Knegt, s., (2012), ‘Welfare assessment in young pet rabbits and guinea pigs in the Netherlands,’ Dissertation Utrecht University, 1-67

Hoeffer, H. H., (2006), ‘Urolithiasis in rabbits and guinea pigs, Proceedings of the North American Veterinary Conference, vol 20, 1735-1736.

Lee Y., (2010), ‘Guinea Pigs,’, ed Tyner, V. V., Behavior of Exotic Pets, Chichester, UK, Blackwell-Wiley, 78-90.

McBride, A., (2011), Guinea Pigs. Understanding and caring for your pet, Magnet & Steel.

Merck Veterinary Manual (2013), ‘Guinea Pigs: Rodents,’ Exotic and Laboratory Animals, 1-8. Available from http://www.merckmanuals.com/vet/exotic_and_laboratory_animals/rodents/guinea_pigs.html?qt=Guinea%20Pigs&alt=sh . Accessed 4 December 2013.

Orcutt, C. J.(2005), ‘Guinea Pig and Chinchilla Basics,’ Proceeding of the North American Veterinary Conference, 1355-1357.

Reinhardt, V., (2002), ‘Comfortable Quarters for Guinea-pigs in Research Institutions,’ in eds Reinhardt, V., & Reinhardt, A., Comfortable Quarters for Laboratory Animals, Ninth Edition, Washington DC, USA, Animal Welfare Institute, 38-42.

White, S. D., (2013), Rabbit and Rodent Dermatology.  (2003) Available at www.gvma.net/files/ECV3013/White-Rabbit_Rodent_Dermatology.pdf  Accessed 31 December 2013.

Wolfensohn, S. & Lloyd, M., (2003), Handbook of Laboratory Animal Management and Welfare, Third edition, Oxford, UK, Blackwell Publishing.


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