There are two problems with doing what you want to do.  First, green milo contains prussic acid.  They would need a very limited intake of green milo compared to the rest of their diet.  Second, there is still a risk of nitrate poisoning anytime the plant is growing.  All drought does is help concentrate the nitrates into one are of the plant.  A rain boosts the nitrates as the plant goes back to growth stage.

I always see the best bet on milo is to check the stems for nitrates to determine height of the nitrate concentration.  Swath the milo above that point as the dry down prior to baling will help eliminate the prussic acid problem.

Maybe someone more knowledgable can give more specifics, but this follows advice I have been given by a cattle research specialist.