OK. Since you have hay in the silo, what you have to do so they can actually eat it is to take the hay from the feeder and put it into the trough in the back by clicking on it with the hay. The hay should then appear in it, 1 piece of hay per animal, and they will eat it and be happy again
it should look like this:
View attachment 4703
(not my photo, got it from FANDOM)