kale

My boys are quite partial to a bit of kale now and then but I was wondering if it’s high in calcium? I’m not too sure and I don’t want them to have kidney problems or anything. How often do you feed kale to your piggies?

:help: I have been feeding my guinea pigs kale, romaine lettuce, bell peppers and carrots. But, when researching if kale stems are okay, I ran into a few sites/people that said kale should be fed once a week or two weeks even and that it isn't good for them? I was wondering if this is true...