Agree with the others.
Bloat is not _supposed_ to be a problem if there is 40% something else for them to eat, sounds like you have that covered with the OG. However, chaning their feed always presents a slight risk, so you have to judge....
Harvesting the alfalfa short now might slow it down in spring. In short, harvest it now, or harvest it next year, might not see much more total tonnage. But harvesting it now and you have it, see what next spring brings and you might get more. Don't know until you try.