Each guinea pig will require both fresh and dry food every day, as well as an unlimited supply of hay. Exactly what fresh food you choose to feed them will determine how much food they’ll need, but a good guideline to follow is roughly one cup of vegetables per pet per day. Fruit should be given sparingly, as it’s very acidic and can cause sores around your guinea pig’s mouth. Some owners advise keeping the dry food bowl constantly full so that your pets can graze throughout the day, but others recommend about one quarter to one third of a cup per pet per day, with perhaps slightly more if it's a bit cold outside, they've been ill, they are young or if they have been pregnant or suckling recently.
Dry and fresh food is necessary for a balanced diet
If you notice that your guinea pigs are getting a little on the chubby side, then you might want to reduce the amount of dry food you're giving them. Try limiting it to one quarter of a cup per pet per day at first for a few months, and then if the problem persists, try reducing it a little bit more. Continue providing unlimited fresh hay and vegetables as normal during this period of dieting, and obviously stop offering treats.