I sprayed the edge of mine with "Bitter Spray" you get at the pet store, made to spray on dog and cats on their wounded areas so they dont lick or chew their bindings and medical wraps while healing. Its like a bitter apple spray, lasts a long time in the piggie cage
Also I give piggies cardboard to play with all the time, just make sure there is no printed stuff on it (ink) or stickers.
Otherwise, lets be real here, saying thats bad for them could be an extreme opinion. You're not giving them something out of a trash can.
Anyone can be skeptical on whats good/bad for your OWN babies in that regard.
I'm a bit of a naturalist, I give my pigs dirt, grass, WOOD (man people here hate that I do that) they are our babies but also animals, cardboard is just paper, relax, its A-OK :crazy:
♥ Sugar