I was just in my chicken house for a minute to check on the chickens and I noticed something smelled really bad, and as I was leaving I noticed one of my hens' vent; the area around it was red, and there was yellow on it, and it seemed to be open. I'm really not sure what this is, and I'm worried that it could kill her or spread to the other chickens. What is that and how to I fix it? I had a rooster die the other day from some unknown reason, and I'm worried that he had the same thing and it killed him. Help!