Even if it is kept in a barn out of the weather and stays clean and dry, it still loses most of its nutritional value. The current years cutting is always better than last years. If you want to feed it up you can it will be good for mid day feedings or a horse that is on a diet. Fed with a little quality hay/ or grain supplement it can still be used. I have had year old hay that has been kept properly. I ended up giving it to them free choice (our horses are on dry lots, no pasture) and supplemented them once a day with a flake of this years cutting/ or with a grain supplement. They did fine.
Hope this helps

You could always sell it off as cow hay also, but if it is still fairly green I would feed it.