Thanks for replying!
We have been putting several flakes of hay in multiple areas, not just in the feeder. But what usually happens is, Hiccup will chase Shiloh, who then gets ticked and chases the goats. I can't remember if I already wrote this, so sorry if I'm just repeating myself.
He still does act like a stallion. Earlier this spring, he kept mounting Bubbles, who couldn't take it due to a permanent injury in his leg. So we separated them until Bubbles gained more weight, which he thankfully has. He's nearly at the normal weight he should be at, though not quite.
He doesn't like being tied. I hitch him for grooming, and he gets annoyed. But he enjoys being groomed (he's our only horse that does). We could try it until he gets the idea.
We'd like to separate them, but we couldn't until spring, since it would require building a new fence for the goats (there's about an acre that is too uneven for horses, but great for goats), and we can't put posts in the ground this late in the year.