The suitable feed for guinea pigs are complete feeds, especially for guinea pigs based on seeds and grains. They should have Timothy or grass hay that should be available for them at all times because the fibre content is crucial for dental wear and gastrointestinal tract function. Guinea pigs need to be supplied with Vitamin C in their diet. Non-breeding guinea pigs need 10mg/kg of vitamin C a day and breeding guinea pigs and/or ill guinea pigs need 35-50mg/kg per day.
Guinea pigs can have fresh greens for additional Vitamin C, these greens include Asparagus. Basil, Broccoli, Brussels sprouts, Carrots, Cauliflower leaves and stalks, Celery, Coriander, courgette, cucumber, Parsnip, radish, red cabbage, rocket, Spinach, turnips, tomato, water cress, kale, cabbage, dandelions (moderation) and parsley. These greens also serve as enrichment for the guinea pigs. Guinea pigs should not have potato and potato tops, Rhubarb (and leaves) and tomato leaves.
Guinea pigs can have fresh fruit as well but only occasionally and in small quantities because there is a high sugar content. The fruit that are suitable in small amounts are apples, grapefruit, strawberries, gooseberries, kiwi fruit, mango, orange and tangerine. There must be careful consideration for expiry dates on complete pellets because vitamin C is perishable.
Any dietary changes must occur slowly mixing in with previous food to avoid any gastrointestinal upset.