The way I see it, with oats you have 3 chances for the weather to co-operate. If you can get it cut at early boot stage and get it cured, you will preserve all of the leaf and have hay that will rival alfalfa. If that doesn't pan out, you have a chance to get it at dough stage. Will loose some digestability and lower leaves but I suppose that loss is made up by the immature grain in the head. If you can't get it at either of these two stages you can combine it for the grain. Dad used to bale a lot of it at dough stage and cattle do well on it. He even won some blue ribbons at hay shows with it. Biggest problem for us now is that rust hits it pretty hard in our area so I don't bale it for hay anymore, I just graze it out.