Warning: Do not change your pet's diet suddenly. Always make changes slowly and one at a time to avoid digestive upsets. If your pet develops diarrhoea feed hay and pellets only and take him to see the vet - it may be nothing to do with his feed. If you have an elderly pet that has always done fine on the feed it is getting it may not worth changing things at all. If you have any concerns about your pet's health he needs to see a vet as soon as possible.
I have recently split this page from the one on feeding chinchillas and degus as guinea pigs are slightly different, and considerably easier, to feed. Much of it is also relevant to rabbits, but since I have little experience with them can I recommend the pages by the Rabbit Welfare Association if you want more information. Also have a look at the rodents and chewing page and the teeth and emergency feeding page for more information about teeth health. although these are written more with degus and chinchillas in mind.
Make any changes slowly and one at a time
Most of the diet should be good quality hay
Limit the amount of pellets fed and always feed guinea pig pellets
If you feed mix do not replace until every scrap has been eaten
All small rodents like and need fresh vegetables
Don't feed commercial treats except ones based on dried herbs
Dried grass and herb products are good supplemental feeds
Supplementary Vitamins and Minerals are not normally needed
Rodents have teeth that grow continually; not just their front teeth, but their molars at the back. This is because their diet is naturally tough and requires a lot of chewing - if their teeth did not grow then they would soon wear out. In captivity this means they need appropriate food that mimics their natural diet. Teeth problems can be very common, generally in chinchillas and degus, but are also a risk in rabbits and guinea pigs. The problem is likely to be a combination of their longevity in captivity, bad breeding and pet foods just their diet just not giving the molars enough wear. There is little that the pet owner can do about the former, but you can prevent malocclusion due to poor diet.
Hay and Forage
Some people get very uptight about the relative merits of pellets, but the most important thing is plenty of good quality forage food such as hay. The majority of the diet should be a good quality hay - I find that a good quality Timothy Hay such as Oxbow Western Timothy is liked best by small and furries and this encourages them to eat more. The guinea pigs even prefer it to their pellets. This type of hay cannot be grown in the UK and has to be imported which makes it quite expensive. It is possible to buy it in bulk on the Internet if you shop around. Try the pet shopping page for some online sources.
However it is very expensive and Guinea pigs tend to be less fussy about their hay than chins and degus, so UK grown timothy hay or a good quality meadow hay, which can be bought from horse feed suppliers by the, bale is absolutely fine. Hay should smell sweet and not be dusty or musty when the bale is broken. For some reason the stuff sold bagged in pet shops for small pets often doesn't seem to be very nice.
Another type of forage that is very popular is alfalfa (or Lucerne). There is a lot of discussion about it being too high in calcium to feed daily, and again people tend to get terribly uptight about it. The theory being that the high level of calcium/oxalate can cause kidney or bladder stones. It's almost a folk lore thing passed down through web sites and the generations of guinea pig and chinchilla keeper. I'm not convinced that there is any good evidence that urinary stones are linked to calcium or oxalate in the diet from plant sources (over using mineral supplements might, however, cause a problem). In fact high levels of oxalate actually inhibit calcium absorption. Generally these are more likely to be caused by a problem, such as a tumour or kidney problem messing up the balance of calcium in the body. In humans the only proven dietary link seems to be too much sugar - so another reason to avoid the commercial pet treats. If you are concerned, then restrict it to a couple of times a week in fully grown animals (growing animals can have more). But it's certainly not something to get worried about as an ingredient in pellets provided the majority of the diet is made up of good quality hay/grass. Sometimes you have to make educated choices - I find Oxbow Alfalfa Nibbles invaluable in animals that are off their food. But I suspect that it can lead to weight gain in guinea pigs as it is so popular - so another reason not to feed it every day.
Guinea pigs are natural grazers and grass is the idea forage. Ideally they would spend all day out grazing on the lawn in summer but, due to the risks from urban foxes and our glorious weather this is rarely practical. Grass can also be picked for them (but don't use grass clippings as they ferment quickly). If you don't have access to a lawn consider whether you have space to grow some in a grow bag or pots. Take care when picking from the wild to ensure that the grass has not been fouled by a dog, or is too close to a road or other source of pollution. Dried grass such as readigrass or supa forage excel is also available and is also a suitable forage for guinea pigs.
Help my pet won't eat hay!
It's unlikely that you will find a guinea pig that doesn't like hay but I've left this section in just in case.
Ideas for increasing intake include:
Look at how much other food they are getting - they just may not be hungry enough.
You may need to consider no treats and reducing the pellet ration for a while. For healthy adults it may be practical replace pellets with a bowl of dried grass on alternate days.
Try a different hay - the one you have may not be that nice or fresh
Having a range of different types of hay might help encourage intake
Put hay in lots of places around the cage where they can have a quick nibble
Try hay and straw chew-toys - or make your own. For example, bunches of hay can be suspended or stuffed in toiled rolls.
I've never met a rodent yet that wouldn't eat Oxbow Alfa Nibbles - but see comments on frequency above
If your pet is eating poorly generally then a visit to the vet may be in order.
Always feed guinea pigs guinea pig pellets as these contain the vitamin C that they need in their diet. The pellets and mixed feed that are sold for Guinea Pigs are designed to have all the nutrients that they need, but crumble easily and do not provide much wear for teeth and are usually too high in protein and low in fibre. It needs to be bourne in mind that these foods were developed in the days when people kept rabbits for meat or showing, and then these were adapted for guinea pigs. So good growth and plenty of muscle and fur in youth where what was required, not long term good teeth and gut health into old age. There is a lack of good scientific research into what makes a good diet for pets, as there just isn't the same money in it as feeding cats and dogs, so it is often a case of trying to mimic what is believed to be a natural diet. In the wild these animals get a lot of exercise and graze continually on low quality grass and plant materials. I love Galen's Garden's description of the average rabbit being "the equivalent of a couch potato living on junk food, with or without good BUPA cover if things go wrong".
Mixed feeds look appetising to the owner, but can cause the additional problem of selective eating. The vitamins and minerals are often in the pellets - which are the bits most often discarded. This can be overcome by using a small amount and not replacing it until every scrap has been eaten, but it is important to make sure that disliked bits are not just dug out and discarded on the floor. Generally a pelleted food is a better idea. Try to buy a good quality feed, in an enclosed container and use by the use by date to prevent it loosing nutrients. When comparing pellets go for a pellet that is lower in protein and higher in fibre.
However, pellets are an important part of a diet as and, as previously mentioned, they contain the vitamins and minerals your pet needs. In fully grown adult animals of healthy weight the best idea is to limit pelleted food or mix to encourage more hay to be eaten. Toys such as treat balls are also useful for guinea pigs as these make them do some work for the food - I don't use a bowl at all and Smudge and Indy have to work for their dinner. Pellets can also be hidden around the cage to encourage natural foraging behaviour.
The big question is just how much you should limit pellets - some rescues recommend only feeding rabbits pellets on alternate days, replacing them with a dried grass such as readigrass or supa forage excel on the other day. Because the guinea pigs really like the hay and have to work for their pellets in the treat balls I don't tend to restrict them.
I like to feed quite a lot of fresh veggies as no matter how carefully you put known vitamins and minerals into a pelleted food you can never replace all the antioxidants and phytochemicals in fresh food. Make sure that all vegetables and fruit fed are of good quality and not rotten, moldy or damp. Be careful about the amount of fruit fed as you'd get an upset tummy if you at a lump of fruit the size of your head!
It has always been common practice to feed veggies to guinea pigs and so isn't controversial like feeding them to chinchillas. They enjoy a wide range including greens, broccoli, peppers, carrots and fruit such as apple. They also love fresh grass (not grass clippings as these can ferment in the stomach ) and safe wild plants such as dandelion (in moderation) and groundsel. There are lists of safe plants on the Internet - I couldn't manage to track down one whilst writing this but it's always worth asking on a forum (search to see if it's already been asked first). Always make sure that anything collected from the wild isn't moldy, isn't picked from anywhere close to a main road where it can get polluted or has been fouled by a dog. And give it a good wash before feeding. The rule is that if you are in doubt then don't feed it. Mine always wheek their little furry heads off when dinner is being prepared because they know that all the spare bits such carrot and pepper tops and cauliflower leaves are coming their way. I've had to stop my practice of opening the kitchen door and lobbing it into the pen as Smudge comes towards you at high speed and can get hit by flying food.
If your guinea pig hasn't been fed a lot of greens then build up slowly. Guinea pigs seem to be more grazers than chinchillas and degus - they are best out on the lawn all day grazing on grass and brought into their cage for hay and pellets at night. Make sure that they have access to water and shade and are safe from predators when out - urban foxes can be active during the day in town gardens so make sure your pet is safe. Piggies with pink ears and noses also need to be protected from sunburn.
Generally my advice on commercial treats can be summed up as: don't buy them. Particularly the stick seed treats and sugary 'yogurt' drops. A much better treat for guinea pigs is some nice fresh grass, dandelion or greens. However, there are a number of specialist treats available that are suitable. These include different types of hay, dried herbs, vegetables and flowers. Avoid any with grains in though.
It's worth bearing in mind that if you have a lot of members in your household your pet may be getting multiple lots of treats - try to come to agreement about how many treats and who will give them. Oh and keep treat pots away from small children and visiting adults who have had a drink as this only leads to spherical rodents.
Your pet should always have access to unlimited, clean water from a bottle. Bowls can get dirty and tipped over and shouldn't be used. Bottles should be cleaned and replaced regularly and never allowed to go green as the algae allows bacteria to grow. One way to remove algae is to put some rice and soapy water in the bottle and shake vigorously. Make sure it is rinsed well and all the rice removed when you have finished. Sometimes it is just easier to chuck and replace the bottle though! I wrap a sheet of paper around my bottles to keep the light out and prevent this but of course it's great fun to pull the paper into your cage and rip it up. In the UK tap water is fine - some people use bottled water but, since there are no standards for the quality of bottled water, it is actually more likely to contain harmful bacteria than tap. If you want to use a water filter ensure that the filter is changed regularly as these can also be sources of bacteria.
Vitamins and Minerals
As previously mentioned pellets contain all the vitamins and minerals needed in the diet. Generally any kind of vitamin or mineral supplement is unnecessary and could result in a toxic overdose if not used carefully. Don't use salt licks as small herbivores have evolved to instinctively lick sources of salt which are very rare in the wild. Free use of a salt lick will result in them getting too much - it has already been added to their pellets. Always use guinea pig (not rabbit) pellets for guinea pigs as they cannot make their own vitamin C, which is added to these pellets.
Vitamin D is an important vitamin and is used to absorb calcium. In the wild much of the vitamin D will be produced by exposure to natural light but an animal living indoors will need to get this from their pellets. I've heard vets theorise as to whether lack of natural light may be in some way to blame for teeth and bone problems in small animals. Guinea pigs benefit from time out on the lawn grazing on their natural food in natural light. Under no circumstances leave your pet with no way of getting out of direct sunlight and they could overheat and burn. And beware of the neighbours cat or urban foxes.
It isn't kind to overfeed your pet and allow them to get fat - in many ways it's as unkind as underfeeding. There are a number of health problems associated with a pet being overweight:
Reduced ability to get around - leading to reduced activity and a vicious circle.
Finding it difficult to keep clean - particularly bottom cleaning.
Increased risk of diabetes and heart disease, which will lead to ill health and reduced life expectancy.
Increased risk of fatty liver which is a serious condition where fatty infiltration of the liver interferes with its function.
Strain on joints and increased pressure on feet which can increase chances of Bumblefoot (nasty sores on the soles of the feet).
Warning: Under no condition starve or seriously reduce you pet's food. Small herbivores need to eat continuously to keep their gut functioning and should have access to good quality hay and clean water at all times.
As discussed above, you can cut out treats and reduce pellets encouraging your pet to munch on lower calorie good quality hay and vegetables for more of the day to prevent and reduce obesity. There are special 'light' pellets available for rabbits but I've not seen these for guinea pigs. Look at the ingredients and try to get a pellet that is higher in fibre and lower in protein.
However, one of the best ways of keeping your pet trim is to make sure that they get plenty of activity. This is particularly the case if you have one pet that is overweight and the other that is normal or underweight as can sometimes happen, for example when you have one with teeth problems. Guinea pigs should be allowed the opportunity to get out of their hutch daily, or be provided with a large enough cage so that they can run laps. See the guinea pig cages page for more information.
Plenty of toys can also help to increase activity - see the environment enrichment page for more details. Animals kept on their own can often get a bit bored and depressed which can lead to them getting overweight - a friend will liven them up but you need to make sure that you have researched what sex/age is suitable and how to safely do introductions first. It's always amusing to see the difference that being introduced to a youngster makes to a rather staid middle aged animal.
One final thing is that sometimes an animal bullied by a cage mate can put on weight. It almost seems that they don't know when they will be chased away from food and so eat as much as possible just in case. I read an interesting study a while back about blue tits in the wild, which theorised this as the reason that dominant birds were leaner than others. If you suspect that there is bullying going on make sure that you have multiple sources of food in the cage and increase the number of hiding places to allow them to get away from each other.
Help my pet is loosing weight/won't eat!
I like to weigh your my pets once a month. Once they have reached their full adult weight, I try to ensure that they get enough food and exercise to keep their weight stable. An unintentional weight loss of more than 10% (e.g. 80g for a 800g guinea pig) should always be investigated by a vet as it can be an early sign of health problems.
If your pet is not eating at all and won't even take their favourite treat then the situation is urgent. They need to see the vet as an emergency as it is nearly always a sign of something serious and once the gut stops working and it is very difficult to get it going again.
This page is really all my own opinion based on my own experiences, a lot of reading, talking to other owners and my evidence-based knowledge of nutrition. It is very easy to get terribly confused and uptight about what we feed our pets with all sorts of information from all sorts of different sources, with many people advocating certain feed regimes with almost religious zeal. Although a good diet can help improve the health of small animals the vast majority of illnesses in small animals are unconnected to nutrition. It's worth trying to give your pet the best diet that you can - but please don't think that if your pet gets ill then it's your fault. We all just do the best we can.
I remember a few years back being harranged on guinea lynx for feeding supa guinea excel to my guinea pigs because it is alfalfa based. I was desperately trying to find out if anyone else had experienced the serious health problem that one of my piggies had. Several people there implied that it was my own fault for feeding such an inferior pellet. It really upset me, especially when no-one there seemed to have any idea about the real causes and just assumed that I must be mistreating him. My guinea pig's problems was sadly most likely due to a congenital heart defect and there was little that myself, or my vet could have done for him - but I really could have done with support at the time.
If you are concerned about your pets health always take him to a qualified vet who is experienced with small animals: anyone who tells you otherwise is an idiot. However, not all vets are experienced with, or interested in, small animals so don't be afraid to find a second opinion.