If you want to offer a whole cabbage, I would offer a whole cabbage and watch.
Unless you have a really enormous flock, they will not eat that whole cabbage all at once.
They will eat some, and go do other things, and the whole cabbage may actually last for several days.
Even when the cabbage is "gone," it may not all be inside the chickens. Some parts may get ripped off, then dropped in the bedding and forgotten.
If chickens have something available constantly, they will self-regulate their consumption. This works for oyster shell, for a complete feed, for a large grassy lawn, and so forth.
That self-regulation may not be at the perfect level, but it will usually be a level that avoids obvious problems.