I hate to say this, but it pretty much looks like our horses' necks did when they came down with dryland distemper (pigeon fever). Your vet can tell you for sure, one way or the other. Our bunch all recovered just fine, but were a mess for a while...
Yikes! Poor baby. He needs a vet asap, those don't look good!
Did these recently appear or have they been there for a few days/weeks?