Your piggy needs three main types of food: dry pellet, fresh vegetables and hay.(and water of course)

Pellets: 

Pet stores are usually abundant on guinea pig mixes. However, it is easy to get carried away by all the different brands. I personally recommend the best: OXBOW's timothy/alfalfa based pellets. OXBOW is a very well known small animals food brand, please check out their website on the LINKS. For young cavies less than 1 year old, feed Oxbow Cavy Performance, which is alfalfa-based, high in fiber, protein and calcium, very important for growing piggies. For adult pigs, feed Oxbow Cavy Cuisine, which is timothy-based, which is more suitable for mature pigs.

You will notice that there are 2 types of dry mixes: the pellets and the mixes.
Pellets look like this:

 
Mixes look like this:
 

Please DO NOT feed your pigs the mixes, no matter how delicious and exotic they look. Those are not nutritionally balanced, and your pigs will not be able to get all the necessary nutrients. Simply feed plain pellets, Oxbow is a good brand.

Reminder on pellets: please do not buy rabbit pellets. Sometimes when pet stores are out of stock on guinea pig pellets, they still want to make money from you so they sell rabbit pellets to you. why are they called rabbit pellets? Because they are obviously not formulated for guinea pigs....rabbit and guinea pigs are totally different animals with different nutritional requirements. Rabbit pellets will not have the correct amount of Vitamin C for your pig, and may contain antibiotics harmful to your pigs.

Storing pellets:

Have you ever opened a packet of cereals and left the bag open for a day or two, so that the next time you eat it it's become a little soggy and not crunchy anymore? I suspect that is what happens to our piggy's pellets....which isn't nice anymore for them. I use air-tight containers/jars. These ensure NO moisture gets in, so the pellets are kept fresh and dry.

Fresh vegetables:

Guinea pigs, like us humans, are unable to synthesize their own Vitamin C, meaning they can quite vulnerably catch scurvy when in lack of this essential vitamin. I remember in junior school and learning about pirates, how they get scurvy and rickets due to Vitamin C and D deficiency since there aren't a lot of fresh veggies at sea. But thankfully, OUR world is abundant with fresh vegetables which are best sources of Vitamin C, so we rarely get scurvy thank goodness. However, piggies will need your help!

Many dry feeds will tell you that it has sufficient vitamin C, but vitamin C loses its potency very quickly, especially when exposed to air. So once you open your pack of dry mix, the VC won't last very long. So you MUST supply your piggy with additional vegetables to ensure it gets enough VC!!

Some popular piggy salad choices:

- Parsley
- Coriander
- Carrots
- Lettuce
- Kale
- Bell peppers
- Celery

- Cucumbers

Soak and wash and rinse your veggies thoroughly before offering them to your piggies!

Introduce vegetables gradually to your pig. You might notice your pig will drink less water after eating juicy veggies. This is normal.

As for fruits, they are high in sugars so do not feed too much. Piggies actually do not like foods that are too sweet. Do NOT feed apple seeds they are poisonous!

Poisonous veggies/veggies to avoid:

Potatoes
Rhubarb
Apple seeds

Iceberg lettuce

Mushrooms

Spicy foods

Dairy products

Human snacks such as chocolate

Hay:

Hay is very very important to your piggy's diet because

1) it provides fiber, which is important to keep their digestion tracts working properly and

2) it wears down your pig's continuously growing teeth and

3) it is a grazing food, which is exactly what your piggy needs to do: eat throughout the day.

Your pigs need to have access to endless, abundant hay 24/7.A quick rule of thumb is to give each pig a handful of hay everyday equivalent to their bodysize. The more the better.

A pig will usually eat a handful of hay the size of their bodies per day. Hay must be available 24/7

For young pigs, feed lots of Alfalfa hay, for its nutritional value.
For adult pigs, feed Timothy hay

There are also a selection of other hay, like Botanical Hay, Orchard Grass, Bermuda Grass, Mountain Grass, and Oat Hay. Your piggies will love these too. Hurray to hay buffet!!

Oxbow hay looks like this:

Storing Hay:

Hay ideally should be kept somewhere with good ventilation, cool, dark and dry.  If you buy hay by the bale, please do not destroy the structure of the bale until you are actually using it. The condensed structure ensures all nutrients and freshness is preserved.

Hay should smell fresh and sweet! If it is dusty or moldy, throw it out!

When feeding hay to your pigs, grab a hearty handful and place it in the hay rack. Give the hay a good shake to discard husks and small pieces that may end up in your piggy's eyes when they are yanking out/rooting around in the hay.

Hay cubes:

Hay cubes are NOT a substitute for hay, but I like to drop one or two next to their cozy beds so they can nibble on it just before they doze off for a nap

Water:

Feed your guinea pig boiled water, not tap water. avoid distilled water, it could upset the osmotic balance in them. Some stores will recommend you add vitamin C droplets to their water: don't! vitamin C promptly loses its potency in water, which will render it useless. It could also change the taste of the water and your pig might not drink it very much at all.

Minipuff and Pudding were outraged that the water supply service was late and diligently put on a water strike, like so (note the stink eye...)

Vitamin C supplement:

As I mentioned above, piggies cannot make their own Vitamin C, so we must supplement their diet with VC to ensure their health. Feeding fresh veggies daily should be more than enough to keep their VC levels sufficient, but just as a precaution, I give my pigs VC tablets once a week. I buy the Oxbow VC pills that look like this:
 
They come in 50mg. every guinea pigs needs 10-30mg/kg daily. Guinea pigs will not "overdose" on Vitamin C, so don't worry if you gave them more than is required.

You can offer the tablets to your pigs as a treat. But some pigs might turn their noses up at it, so you can dissolve it in water, then syringe feed. This ensures your piggy ate everything. Some people suggest sprinkling the tablets into their food bowls.

Please do not add vitamin c drops into your pig?s drinking water.

Please feed your piggies Vitamin C specifically, do not buy multi-vitamins. 

When my pigs are ill, I will give them 2 or 3 tablets of VC to boost their health. Of course this is not a substitute for medicine, but I am convinced the additional VC will help them recover better.

This is my VC kit for the pigs. If they eat the tablet directly, it is the best way because you are sure it is completely consumed. If they don't like it, dissolve it in water, mash it up and feed it through a syringe to your piggies.

You can find syringes at all veterinary clinics.

Wheat grass; a real treat:

Wheat grass is sometimes called cat grass. You can get wheat grass seeds in plant supply stores.
Grass is a guinea pig?s natural food in the wild. Your piggies will absolutely adore eating grass because it is sweet, fresh, juicy and packed with nutrients.

Some devoted piggy lovers will actually go to their garden to trim the grass and then bring them to their piggies.Do NOT cut grass from the sides of roads as they will be polluted by traffic fumes. It can also be sprayed by pesticides, which will be very bad for your pigs. Additionally, there might be dog feces in the grass which will also give your pigs diarrhea.

The best way is to safely grow your own grass is at home, you can buy the seeds at garden supply stores.

How to grow wheat grass:

1) soak the seeds in water for a day in a bowl
2) drain out the water and rinse the seeds, then leave the damp seeds in the bowl overnight
3) the next morning, rinse your seeds again, some of them might have started to sprout.
4) Dampen soil in a flowerpot, then sprinkle the wheat grass seeds on top of the soil. There is no need to bury the seeds
5) Water a little everyday, keep the soil damp but not soaked!
6) Wheat grass usually grow up to 2 lengths your finger, you can simply trim it then offer to your pigs. They won?t stop until they?ve finished every last piece!
7) Wheat grass usually have up to 3 harvests before you can just dump everything out and start over with new seeds

Puffy enjoying his wheat grass. Can you see him literally smiling??

There are many commercial treats out there made for guinea pigs. I don?t think any of them is necessary unless you are talking about VC tablets. Commercial treats are expensive, and not even healthy for your pigs. They contain a lot of fatty sugars, nuts, fruit pieces, which isn?t beneficial to your pig?s health in any way. I even find that my pigs couldn?t care less about those raisin pieces or strawberry droplets?.

** If you do buy commercial treat sticks, be careful not to buy the hamster treat sticks; these usually have sunflower seeds still in their shells, which can be a choking hazard to your pigs?.!!

Salt licks are not necessary, but there is no harm in offering them. Some pigs completely ignore them.