Your guinea pig's well-being depends on what food he / she consumes so it is important to have a varied diet with a wide variety of fruits and vegetables on a daily basis.
Diet There are many fruits and vegetables that guinea pigs can eat. There are also many wild plants that guineas can chew. Like us, they have a preference for what they prefer when it comes to food.
Not provide your guinea pig with everything you would not eat yourself. Green vegetables should be provided daily. Salad may only be offered as a treat, as it has no nutritional value. Spinach is high in oxalic acid, which can interfere with digestion supplied in excess.
Guinea pigs need 10 mg of vitamin C per day. I have discovered that the provision of any of my guinea pigs is 1/8th of a green pepper per day then that is enough for a daily dose. Do note that red peppers are higher in vitamin C, but it is also higher in sugar so green peppers are always best to be fed on a daily basis.
Get rid of all decaying vegetable after a few hours or so. Leave it in the cage / barn is a common cause of diarrhea in your guinea pigs.
Fruit As fruit holds a lot of sugar and acids, it is best to feed them as a treat, say once or twice a week. Honeydew melon and pear are loved by many guinea pigs. Tomatoes can be fed more often. You be careful with citrus fruits as they can cause tenderness mouth.
Forage from nature Grass is much loved by guinea pigs, but never feed grass trimmings from a lawn mower. This is due to the fact that other wild plants like buttercups are mixed in the ordinary grass; contaminate it. Alternatively, you can purchase dried grass from a reputable pet store or horse feed store.
While dried food is not massively important, it provides 5% of the guinea pigs diet. Many people feed pellets as this prevents select feeding. Currently I am using cereal as none of my guinea pig select feed. When changing a little each brand new mix dried with a little old dried. Have to switch gradually to avert any instability in the digestive system.
As always, unlimited hay should be offered. I think twice a day is sufficient. I offer a handful for each guinea pig.
It is always advisable to establish a feeding routine and follow the set times every day. Work out a routine around your own schedule and your guinea pig come to know when it is feeding time for them....