Dietary Components

Guinea pigs are fibrevores

Guinea pig nutrition is a real journey of discovery and such an important one! Insufficient research on guinea pig diets means there are some question marks/debate with regard to some components of the guinea pig diet; in addition you may find some contradictory information. A 2023 clinical review of guinea pig nutrition is available. Exact amounts of different dietary components will depend on many factors such as age, body condition and health status. We do know that cavies are obligate fibrevores - they need to eat mostly fibre for their health. Guinea pig teeth are adapted to an abrasive, high-volume diet; wild guinea pigs eat mostly grasses, which are a low-energy, high-fibre food. Good quality hay must be provided ad libitum - hay and/or grass should make up 85-90% of the diet. Depending on whether guinea pigs are primarily kept indoors or outdoors may mean the amount of fresh grass they have access to will differ, the RSPCA recommends fresh grass as often as possible; for 'indoor' guinea pigs who have not had exposure to grass, a gradual introduction is a good idea; do not give lawnmower cuttings - see section below on hay and grass. Eating good quality hay and/or grass encourages tooth wear (guinea pig teeth continually grow and need to be worn down with the correct diet) and good gut health. There are many different brands and types of hay, some are poor quality brands, which impact piggy health, and some types are more appropriate as a treat - see below for more. Incidentally, you will see that your guinea pigs eat some of their poop, this is normal, it is a source of B and K vitamins, as well as fibre and protein. Guinea pig poop can help us identify if there is a problem with the diet, see more here.

Other components

Fresh veggies and concentrate: To complement the ad libitum grass and/ hay, general advice is that the daily diet should also include some fresh, washed, leafy greens/veggies, some wild plants (see below) and a small portion of good quality, high-fibre concentrate (called nuggets or pellets by manufacturers). Make sure the concentrate, i.e., nuggets, states 'for guinea pigs' (NOT 'for rabbits') - guinea pig nuggets are formulated with added vitamin C, which is required by guinea pigs. Rabbit nuggets don't have the added Vitamin C. Piggies, like us, need Vitamin C in their diet as their bodies cannot make it. A tip is not to make the mistake of buying an extra big bag, thinking it will last longer and be more economical - Vitamin C degrades quickly (>50% in 3 months), so if the nuggets are hanging around unused for a while, they won't be fulfilling the purpose you bought them for. It is wise to pay for good quality food to help prevent costs associated with poor health later on. Buy sealed bags and keep them sealed - I use clips to make sure the bag is airtight.

Wild forage: You can provide wild forage and edible tree twigs/small branches (as long as safe to feed) for guinea pigs to gnaw. In the UK, national animal welfare charities provide resources on what 'wild forage' is safe to give guinea pigs, i.e., which wild tree species or other plant matter that can be fed. Woodgreen Animal Charity has a section on their website: 'Foraging wild and garden plants for your guinea pigs'. Always consult your vet to discuss diet, they often have handout diet sheets for guinea pig owners. Scatter feeding rather than just providing food in bowls will mean piggies have to move around to find their food, this encourages movement and use of senses to forage, which promotes phyical and mental health; it also discourages selective feeding; we want to encourage diverse feeding with lots of hay consumption. Diseases such as osteoarthritis have been linked to guinea pig enclosures that are too small, and without sufficient enrichment to promote movement.

Muesli-type feed: Bags labelled ‘complete guinea pig food’ or similar, often contain muesli, so be careful as muesli is high in energy but low in fibre, and high in sugar or starch, which isn't beneficial for maintaining gut health. Muesli also promotes selective feeding of more palatable items, resulting in an unbalanced diet.

Fruit: Concerns regarding sugar and acidity, mean that some bodies don't list/consider fruit as suitable; for those who do consider certain fruits ok, this is only if fed as an occasional treat. Note that although orange is sometimes listed as ok, it is a citrus fruit - be mindful that citrus acidity can affect the delicate skin of piggy mouths, so the RSPCA (UK) advise against this.

Treats: Be aware that piggies have a low sugar tolerance, be mindful of certain 'treats' such as honey and seed sticks, often sold in shops, these can be high in sugar as well as chemical colourants (also unhealthy for guinea pigs). Rather, go for natural forage treats to scatter around such as dried herb mixes.

Variety and balance in the diet is very important for gastrointestinal health - scientists warn against giving too much of some components; as an example, Edell et al. (2022) warn against inappropriate diets composed of mostly alfalfa or nuggets/pellets. Introduce new food gradually and always seek advice from your vet about diet, changes needed will depend on the health status of your piggies, your vet will direct you accordingly. The UK Pet Food guinea pig nutrition poster is a quick visual of how much hay/grass should make up the diet and foods to avoid.

Hay and Grass

Piggies need grass and/or high quality hay to eat and good quality hay for bedding/refuge.

Hay: quality is not always obvious to new piggy owners. Here are some useful ways to identify good hay:

Good hay should be dust-extracted, it should not be too dry, dusty, short-chopped or crumbly.
It should smell sweet and lovely - not musty, as this indicates the presence of fungal spores.
It should not be brown and generally 'old' looking.
It should have great colour, think lots of lovely green shades!

Over time I have tried a wide range of hays, I have now selected companies who produce very good quality hay, which has helped my piggies' health. Avoid hay which is very broken or chopped into fine, small pieces of hay, these are not great for feeding or bedding and tend to get in piggy eyes. Poor quality hay can also lead to poor nutrition, inappetance, allergies, or irritation of respiratory membranes, followed by respiratory disease. Provide fresh hay daily, different hays keep foraging interesting - I use a mix of Timothy, Meadow and Orchard hays. Although Timothy hay is an ideal feeding hay, important for teeth and tummies, a 2020 study found that only approximately a third of piggies were given this daily. Other hays include ready grass, alfalfa and oat grass, but these are different in composition, so consider these as a treat - for different hay types explained, have a chat with your vet. Scientific sources which discuss hay types and health conditions include Edell et al. 2022, Azevedo et al. 2022, Witkowska et al. 2017, Hoefer, 2006.

Hay poke

Be aware of hay injury to their eyes or otherwise known as ‘Hay poke’. It is not necessarily an actual poke, but often due to small bits of very broken up hay, getting into the eye. Be mindful that some hay packets can be composed of crushed, short-chopped hay, which presents hundreds of tiny fragments - these easily get into guinea pigs' eyes. Even tiny seeds from good quality hay could get into eyes, so it is worth minimising the risk by not buying cheap, low grade hay that is chopped into small bits. I have found that finding a good quality hay has significantly reduced the incidence of hay poke in my piggies. Injury to the eye is caused by hay damage to the eye itself or hay getting caught under an eyelid, which is extremely painful. Injury will cause ulceration, which if not treated can lead to a piggy losing its eyesight, or the eye itself. The fact that it is very painful is worthy of treatment in itself; it is an urgent situation which requires veterinary treatment.

Grass: A gradual introduction to grass for primarily 'indoor' piggies is a good idea because the sudden introduction of a new food/overindulgence can lead to 'bloat' (see below); they may not be used to eating grass so their digestive systems will need a gentle introduction to it - pick some from the garden to give them and increase slowly. Picking is similar to how a piggy would naturally eat grass, pulling at stems and grazing - do not give mown grass, this damages grass, it is short-chopped and ferments quickly, which can cause gut issues, even toxaemia. Ensure that grass is untreated with chemicals.

Water

Water must always be available. Monitor how much your piggies drink; water intake is so important - an example of its function is in flushing calcium deposits from the bladder, explained below. Use bowls and bottles because individuals may have preferences. Just make sure that bowls are safe - heavy, accessible bowls so they can be reached but not tipped. Water intake can be encouraged by soaking fresh veggies in water and even putting some on hay.

Healthy forage treats

You can forage for wild plants to provide your piggies, but be careful where and what you collect, see here for advice on this. Although for rabbit owners, a nice guide to help with plant identification is 'Foraging for Rabbits' by Dr Twigs Way. You can also buy purpose-made dried herb/botanical forage (but without additives) to scatter sparingly around your guinea pig's home amongst the hay, such as dried marigold, cornflower, rose, dandelion, nettle or mint, for example. These encourage natural foraging behaviour. Example companies who make herbs for guinea pigs, include 'Piggie Parcels' who offer a wide range of herbs or 'Burgess Excel' who produce some herb mixes. 'Harvest Festival' are dried stem mixes, available from 'Rosewood'. If you wish to discuss herbs with a vet who has specialist knowledge of herbs (the 'British Association of Veterinary Herbalists' have a list for the UK).

Bloat

A useful point to make here is be mindful of 'Bloat'. This is where your knowledge about your pets' personalities and usual behaviours is so useful. With this condition, you will notice that your piggies become very lethargic and do no want to move. You may notice that their abdomen looks bigger or bloated - hence the term 'bloat'. You may see that there is less poo and that they lose interest in eating - very unusual for guinea pigs! The image here shows X-rays of Belle, one of my piggies. You can see clearly on the left of her spine in the abdominal region (area indicated by the white box) a build-up of gas, this is associated with gut stasis (movement within the gastrointestinal tract stops); she had to be treated with medication to increase gut motility. 'Bloat' causes a lot of pain. It is an urgent situation that can become life-threatening so it requires veterinary attention. Sometimes overindulgence in fresh veggies or fruit, grass or clover can cause this. Other causes include eating contaminated food, dirty bowls, food straight from a fridge and sudden food changes.

If you observe the following signs then it may be that your piggy has a case of bloat:

sunken eyes
reluctance to move
distended (swollen/inflated) abdomen
no appetite/refusal to eat
lack of poo
breathing distress

Water and bladder health

Guinea pigs commonly suffer from bladder health issues. Various factors may be at play regarding bladder health, including not drinking enough and dehydration - research is trying to elucidate the causes. 'Bladder sludge’ commonly occurs in guinea pigs, which is a build-up of sediment in the bladder. This 'sludge' can lead to uroliths, otherwise known as 'stones', commonly composed of calcium carbonate. If piggies don't drink enough water, this can result in concentrated urine sitting in the bladder, which contributes to the formation
of stones (see page 4 of Witkowska et al. 2017). Even without stone formation, the 'sludge' irritates the bladder, leads to infection, inflammation and stone formation, which ultimately results in a lot of pain. There may be urine staining or scald on the abdomen, bottom, legs and feet, which unless a guinea pig is checked regularly, may go unnoticed and result in infection/open wounds. The issue may also affect the feaces due to pain in that area. You may notice blood in the urine and sometimes poo will become tiny, very thin or of abnormal consistency. In the case of bladder sludge or stone diagnosis, vets may adjust proportions of high-calcium and oxalate foods in the diet to help manage the condition (see Hoefer (2006)). Encourage water intake because it's likely that insufficient drinking is a primary factor - without sufficient water intake, sediment isn't flushed out the bladder. Hydration can be supported with plenty of water in bowls and bottles, on fresh food, even on hay. Individuals may have a preference to use water bowls or bottles so provide a choice. For more discussion on this subject see Edell et al. 2022 and Azevedo et al. 2022.