I noticed my gelding rubbing his rear on his stall wall about a week ago. Then, I noticed this dirty spot above his tail bone on his rump. When I rubbed it with a brush to clean it, it didn't clean off AND he noticeably tucked his rear end. Attached are pictures to show what it looked like yesterday.
This is the first day I noticed it being scabbed up like this. Before yesterday, he was just sensitive there (from rubbing, I assumed).
Any thoughts on why he suddenly started doing this and what I can do about it? I've washed the area 4 days ago and rinsed him off after every workout. The BM put MTG on it when she first noticed it, but not since.