Feeding kale to a guinea pig once or twice per week is safe. Kale is a good source of vitamin C, which is necessary in a guinea pig's diet. However, it is also a significant source of calcium, which is harmful to guinea pigs in excess amounts.
Guinea pigs should eat twice daily. Timothy hay provides excellent nutrition and fiber for the animal. Supplement with small amounts of various leafy green vegetables, including kale on occasion. Commercial pellets formulated for guinea pigs are acceptable but are not recommended as a sole food. A small daily serving of fruit and fresh, clean water are also required.
Guinea pigs thrive on a consistent diet that provides proper nutrition. Introduce new foods such as kale slowly and gradually to avoid digestive issues.