I have 3 young RIR chicks approx. One of them was sick a couple of weeks ago . By sick I mean he looked weak , didn't interact with the others, seemed to tremble and have some diarrhea. I separated him from the others for a couple of days and he improved. He now acts fine but he has no feathers on his bottom. It's totally bare. Does anyone have an idea what might cause this? Is this an after effect caused by the diarrhea?