Twice now I've noticed some diarrhea and blood spots in my chicken's poop after a rainy spell. I'm assuming the wet conditions allow cocci to multiply and overwhelm my chickens' immune systems -- they were on medicated feed for the first 12 weeks, and now they're 18 weeks. Last time this happened, it was during the time I was switching feeds, so I went back to medicated feed for a little while and it cleared up beautifully (and the rain stopped). This time, however, I'm in the process of switching to layer feed and don't have medicated feed on hand. And I think it'll be rainy for a few months now, before it snows! What should I do?? My local feed store has nothing but sulmet, which makes me nervous.