Guinea pigs under 10 months od age need an alfalfa based pellet. But, if they are an adult they can then safely use timothy hay based food. Now, you don't absolutely HAVE to have pellets for your guinea pig. Fiesta, Kaytee, All Liviing Things, Ecoritions, FM Brown, Vitacraft, and Purina make foods that are not pellets. The best place to find an assorted stock of food is at Petsmart. Their prices are reasonable and the brands they carry are #1 in the country. When guinea pigs ar still growing, they canstantly need a full bowl of food. After that, if you have three guinea pigs about two handfuls of food. If you have one that would be about 1. If you change foods, be sure to do it gradually. By this I mean that on the first day you should have most of your old food in the bowl with a few pellets of the new food. Each day gradually add mor of the new pellets and take out more of the old.
Fruits and Vegtables
Everyday guinea pigs need freash fruits and vegtables. But certain kinds can be dangerous when they eat them. They also need a good source of vitamin c. The best foods to give them are green and red peppers (not chilis), broccoli, kale, carrots, lettuce, celery, dandelion leaves, grass, baby tomatoes, cucumber, parsley, pear, seadless grapes, satsumer, and corn. You can aslo give your small pet apples, but some guinea pigs have a horrible reactions to it up to and including death. It is best when a guinea pig is given 4 types of fresh food every day. 2 in the morning and 2 in the evening.
Water
As it is for all living things, water is one of the most important parts of a guinea pig's diet. They need constant acess to fresh cool water, day and night. The best way to get your guinea pig this water is with a water bottle. They conveinently hang onto the cage and can hold large quantites of liquid. You should wash the bottle at least twice a week. When you clean the bottle, make sure nothing is clogging the whole at the end. If your guinea pig isn't drinking, the whole might also be clogged. You can also use a water bowl. This is best for younger guinea pigs. It is easier for them to reach. The same rules apply. Always have fresh water, clean the bowl twice a week. During warmer weather your guinea pig will drink more, this is when it is even more important to keep the bowl or bottle full. When your guinea pigs are having "free range time" always have water and ffod in the pen as well.
Hay
Hay is seriously important in a guinea pig's diet. Guinea pigs are herbivores. Their digestive system requires high fiber food. This also keeps their constantly growing theeth ground down. It is very important to always have fresh hay. This can be by the bushell from your local equestrian center or just store bought just for guinea pigs. You can also use fresh grass for economical reaons. The best way to give your guinea pigs hay is using a hay ball or rack. It keeps it al in one place. If you just put it on the bottom of the cage it will get dirty and need to be changed at least 3 times a day.