sounds like rain rot
Yup sounds like rain rot. I just got my weanling back (I say I just got him, I mean I went and TOOK) from a horse training/boarding place that I took him to. When I took him they had a nice run with cover, he was in that stall for five days and on the sixth they had moved him into a round pen which was temporary I thought. Well that night started the rains and when I went back he was standing in mudm. I was peeved to stay the least and expressed my displeasure. The guy reassured me he would be moved back, but the horse occupying his stall need separation until a coggins came back which was supposed to be later that day. I went back the next day same situation so I called and said that my baby was leaving, when would he be back to unlock the property. He told me just to turn him out with the herd..mwhich was run by the herd stud. I told him hell no. He made me wait one more day and then I wenand got him so needless to say four days in mud is all it takes.
If you can't give your guy a bath, treat each individual sore daily. Its painful, but you should also scrape them as the fungus can't grow when exposed top oxygen. Hope this helps.