I think so, I had a twisted willow tree in mine and the buns seemed to enjoy nibbling it, they didn't eat a lot at a time but, it didn't do them any harm, if anyone knows any different please let me know as I have chopped it down and saved two large sections of the trunk to have in the runs as jumping/gnawing wood. It grew from 5ft to being absolutely massive, way too big for the garden - I had to resurrect my dog from underneath (we are moving) and I have managed to salvage a cutting to keep in a large pot, not sure if it will work or not but, I hate to think I have killed a tree so fingers crossed it will survive. Stef what sort of willow is it you have?