Oxbow’s Essentials – Adult Guinea Pig Food is made from timothy grass meal, which includes the high fiber adult guinea pigs need. However, it contains a lower level of protein, calories and calcium than alfalfa-based pellets. Adult animalsâ digestive systems do not require the same level as that of younger animals. Essentials – Adult Guinea Pig contains stabilized Vitamin C and an optimal calcium-to-phosphorus ratio that helps maintain a healthy body. When fed with Oxbow grass hays and treats, Essentials – Adult Guinea Pig provides complete stabilized nutrition.