I've tried giving them cactus pad. They weren't very interested. It could be that I didn't try hard enough - but the stuff is a little expensive around here and my leopards enjoy it much more.

I also tried the cactus fruits - but that it is just a big mess.

They really like dandelion flowers and leaves, clover, plantain (weed), wild strawberry leaves, wild violet leaves, and from the grocery store: endive, collards, squash, carrots.