Like I said, I've been thinking it's just rub from the hog panel on the pen and feeders. So he's had it for awhile and nothing else has shown up on the other bucks he's in contact with. They rub heads and necks and all during the rut. Just thought I'd throw it out there in case anyone had seen anything like this. Thought about rubbing an antifungal topical or wound spray on it just for the hell of it.
Going off that last photo I would say that he has a infection or fungus going on also. The solid patch that looks smooth might be from the hog panel but the patchs and spots below that are not just from rubbing.
I have the opposite opinion, I see the rub on top of his neck too and think it must be the hog panels. I have a cow that gets that from her feeder. She is a little too tall for it and it rubs the hair off the top of her neck. If the skin under it is damaged you should still consider infection of some sort. Maybe secondary to rubbing the fence.