I've heard of "Rain rot" as a skin fungus that I've only witnessed on my Brahman cattle. It's a rash they get on their dewlaps and bellies, and as you can tell by the name, it's prevelant when we've had a lot of wet weather.
If you use a funguside (sp?) it will greatly reduce it.. but also some SUNSHINE (which we haven't seen much of) and warmer temps will also make it go away.