I have a small flock of two year old RIR hens. In the passed few months I lost two, both exhibiting the same symptoms: Start looking puffed up, wont return to cook, won't roost up high, dirty poopy butt. And then they become very weak and die. My chickens are free range with some layer pellets available to them. They spend a lot of Tim around the barn and horses, and could be eating oats. Would that kill them? I now have a third chicken with these symptoms. I have taken a few pics that I will post. I soaked her last night and gently felt all around her vent, it feels soft, although her abdomen feels tight.