Taken from guinea lynx in the food section under what is not reccomended:
Avoid mixes or treats with nuts, seeds, dried fruit and dyed pieces.
Do not feed dairy and meat products (cavies are herbivores)
Avoid seeds in husks (like sunflower seeds), which can be a choking hazard.
Do not feed rabbit pellets (they do not contain Vitamin C and some may even include antibiotics toxic to cavies).
Avoid or use sparingly, cruciferous vegetables (cabbage, collards, bok choy, broccoli), as they may cause gas in your pet.
Do not use mineral wheels. Never use Tang (which contains dyes, refined sugars, and very little vitamin C) in drinking water.
Avoid commercial treats marketed for cavies (like yoghurt drops) which can even be detrimental to their health. Consuming these empty calories (many contain fat, sugars and even excess calcium) can result in decreased consumption of the basic foods they really need.