A lot of people seem to like feeding their tortoises prickly pear (Opuntia sp.) cactus pads because they are a good source of calcium. However, it is my understanding that Opuntia are also rich in oxalates. As with other plants, I would think this would diminish the quality of cactus pads as a forage item, making them suitable for occasional feeding, but not very often. What do you guys think?