My horses and a few of the others at the same farm have what people are just calling "fungus." Mostly it isn't visible until brushing the horse's legs and the hair starts falling out. On the lighter horses there is a bit of black speckling that looks like dirt. There is no open skin, sores, scabs, etc. The horses don't appear to be itchy or in pain. I know it can be treated with an antifungal shampoo, but my main concerns are:
1. What is it? Rain rot? We were having a drought until a few weeks ago and it seems like one of the horses had it before we had any rain or dampness. We did have a massive heat wave though.
2. Someone mentioned that they think it is spreading from horse to horse via grooming tools, tac, and horse to horse contact. How contagious is it and how can I slow/prevent the spread?