I saw a mention in another thread (ponds in a greenhouse) that duckweed can be fed to animals. I keep sheep and I have a large pond covered with duckweed. We usually just compost the weed when we drag it out but if it wouldn't harm the sheep I'd love to see if they would eat it. They graze and browse a lot of different plants/trees and even eat grass clippings if we dump them in the field.
Are you talking about azolla? Its great fertalizer ,especially good firing up compost!
they seem to take to it better dry maybe ad salt or grain to get em started