Your guinea pig may be small, but his appetite is large—and it’s important to feed him nutritious, wholesome foods. “The right guinea pig diet keeps your cuddly pet happy and healthy,” says Dr. Amy Kurowski, a small animal veterinarian. Dr. Kurowski explains that guinea pigs are herbivores, meaning they don’t eat meat or dairy, and are hindgut fermenters, which means they are specially equipped to break down hard-to-digest plant material. Guinea pigs possess an enlarged cecum, a pouch in the intestine that contains lots of bacteria to aid in digestion of hay and other tough plants.