They need hay to keep the rumen healthy. Be careful of listeria with the silage. Any mold can hurt a goat. Their rumens aren't
as big as a cow's and they can be poisoned by mold in silage. Soybean isn't real good for goats, either. (In my opinion).
If you post these questions up in "Goat Management", you will get more answers! There are a lot of knowledgeable people on this