Guinea pigs should not eat parsnips as they can be high in carbohydrates which can predispose them to bloat, digestive upset, or enterotoxemia. Additionally, parsnips are not good for their stomachs due to their phosphorous and acidic content, which may cause gas or bloating in guinea pigs. Overall, it is not recommended to feed parsnips to guinea pigs as it can lead to potential stomach and digestive issues.