Guinea pigs are strict herbivores. They should be fed a complete, pelleted diet made especially for guinea pigs that contains at least 16% crude protein. The pellets should not be fed more than 90 days after their milling (check the bag or box for the milling date). Also provide small amounts of grass hay, and supplement Piggy's diet with a source of active ascorbic acid (Vitamin C), such as a handful of cabbage or half a handful of kale (washed and fresh) or a quarter of an orange. Because guinea pigs can't produce their own Vitamin C, you should add a Vitamin C supplement to their water as well - a teaspoon of Vitamin C liquid to 12 ounces of water. The water will need to be replaced daily, however, as the Vitamin C will lose its potency rather quickly.
In addition to the above, the following fruits and vegetables-fresh, washed, and with seeds or pits removed-can be fed as treats:
Also, dandelions, grass and wild clover can be picked from your yard (but only if you're sure they're free from pesticides and herbicides) and offered to Piggy, along with oats or graham crackers. But no more than 10 percent of your guinea pig's diet should be made up of foods other than the pellets. And to be sure he doesn't have a bad reaction to a new food, offer only one new food to Piggy at a time.
Don't feed powdered food; it just gets wasted, and the dust from it can gather around Piggy's mouth and in his nose and cause health problems. No table scraps or other animals' food, either! These, too, can cause health problems resulting from an unbalanced diet.
To prevent obesity and nephrosis (a disease of the kidneys) in older animals, decrease the amount of pelleted food offered and supplement with more hay. In these aging pets, hay can constitute up to 25% of their diet.
Food and fresh water should always be available. Mount feeders and waterers to the cage walls to avoid spills, and only use water bottles with metal sipper tubes, as Piggy will just chew up plastic tubes.
Guinea pigs commonly ingest their own feces, so although you may be disgusted to see such behavior, don't be alarmed! This is normal and provides them with proteins and vitamins.