Guinea pigs may eat a mix of grass hay, vegetables and fruits as part of their daily nutritional intake. Plain, dye-free guinea pig pellets make a good addition to daily feeding.
Grass hay serves as an important part of the guinea pig diet because guinea pigs are grazing animals and the constant grazing helps keep their teeth ground down to an appropriate size. Owners should put fresh grazing hay in the guinea pig's cage each day.
Guinea pigs do not produce their own vitamin C, so a regimen of fruits and vegetables remains an important part of their diet. Green, leafy vegetables are best, but carrots, cucumbers and corn-on-the-cob serve as appropriate alternatives. Apples and pears make good fruits to supplement a guinea pig's diet. However, because of the high sugar content, guinea pigs should eat fruits in moderation, preferably in small pieces once or twice a week.
Owners should never feed guinea pigs spoiled or rotten foods and should remove any uneaten foods from the cage after an hour or two to prevent spoiling. Guinea pigs should never eat cabbage, beans or kale. Raisins, bananas and melons have too much sugar for a guinea pig's diet, and avocado and coconut have excessively high amounts of fat, making them bad for digestion.
Guinea pig owners need to keep a fresh supply of water for the animal by replenishing it daily and as needed throughout the day. Commercial treats can hinder a guinea pig's quality of life, due to the preservatives and fructose they usually contain. Rolled oats make a healthy treat that the animals enjoy. Multivitamins or salt wheels are not necessary if the guinea pig is receiving enough nutrients from a balanced diet.