My horse just developed all these hard smaller sized bumps all on the top of his butt and clustered together, no where else. You can't see them but you can feel them when you run your hand across the area. I was thinking it might be rain rot? We just had a week of rain almost everyday and the temperature has dropped alot, getting pretty cold especially at night. He was just de-wormed last week so I am thinking that rules out ringworm?? but am not one hundred percent sure. Also he was put in an area with weeds to chow down for a few days so am thinking it could have been an allergic reaction? any ideas of what it could be and what I should do to help clear this up? Thank so much I am worried.