Not quite sure where to post this - as its about tubes it should be in "housing", but its about piggies eating them so I suppose I will get away with posting it here! 
I bought a big tube for them yesterday made of cardboard, and it is coated with lots of hay and herbs. My piggies love them - but I am now wondering how they actually make the stuff stick on the cardboard, and whether or not its safe for piggies? Does anybody know what is use as an adhesive?

I bought a big tube for them yesterday made of cardboard, and it is coated with lots of hay and herbs. My piggies love them - but I am now wondering how they actually make the stuff stick on the cardboard, and whether or not its safe for piggies? Does anybody know what is use as an adhesive?