Horse has round bare spots the size of nickel on his hip and mid-barrel?

While petting my colt, I noticed a spot of hard, matted hair on his hip. When I pulled, the hair came out in my hand and left a completely round, bald spot about the size of a nickel. I started feeling around, and noticed a couple more of these matted spots. The hair tuft that came out had what appeared to be dried pus??? on the edge that was attached to the body. The spot itself is completely bare of ANY hair and is almost perfectly round; it does not look like a scab, but neither does it look red or painful. It is simply bare skin. He had not been scratching, biting, or rubbing, neither does he seem to be itching. He did not seem to mind having the hair pulled or the spot touched. Also, there is white, flaky stuff in his mane, and I am panicked that it may be lice. I've looked for bugs or movement, but I haven't seen either. The white stuff is more flaky than it is beaded. Could this dandruff? Or is it possible lice? And could it be connected to the bare spots appearing on his coat? Any idea of what is causing this? Or how to stop it? Or get rid of it? Thanks for any help you can give!