Different kinds of pocket pets have very different nutritional needs. So, like people, guinea pigs need to get vitamin C from fresh fruits and vegetables in their diet. Some manufactured guinea pig diets may advertise that they contain extra vitamin C, but the vitamin breaks down over time. After about 90 days, the vitamin is no longer effective, so it's important that you feed your guinea pig fresh foods rich in vitamin C like kiwi fruit, tomatoes, oranges, carrots, broccoli, and kale. You can also purchase a vitamin C supplement that you can add to your guinea pig's water at a concentration of about 200 milligrams per quart of water.
Chinchillas require a lot of plant fiber in their diet.
They should have a supply of fresh dried hay or timothy grass to eat throughout the day. The hay should be supplemented with a measured amount of chinchilla pellets, given in the morning and evening. Chinchilla pellets can be hard to find, and they may have to be specially ordered in some areas, but rabbit and guinea pig pellets are too short for chinchillas to hold and eat. The extra effort is worth it for a happy chinchilla. Rabbits also require special attention to the fiber in their diet.