I've never fed cabbage before but put whole heads in each day pen the other day and they were mowed down to an apple size by PM chores.
I left them whole to give them something to chew on. I put them in a high sided black rubber horse feed tubs so they didn't just roll it around in the dirt.
They go nuts over watermelon eating it rind and all. Not much nutritional value I suppose but they love it.
I also have some new weed grass growing up thru the mulch in my veggie garden so I've been picking that and giving it to them but its not in large amounts
so it more like a little green snack.