We have 3 hens who are about 8-9 months old that live in our coop. We have a leghorn, a rhode island red, and a golden laced wyandotte. We also have 2-3 month old hens. A barred rock, a black sex link, and an ameracauna. We had been keeping the three younger hens in the garage in their own pen; but, my dad, who has raised chickens most of his life, came over last weekend and said they were big enough to merge with the older ones and he told us we should be able to just put them in. Yeah, he was wrong. I'm thinking since he didn't see them side by side he misestimated the size difference. The first day went okay; but, today the Leghorn just went crazy. The little ones have been hiding behind a board in the coop that the big ones can't get behind. At some point the Americauna ventured out and I caught the Leghorn chasing her and than standing on her pecking. The Leghorn didn't get off until I shushed her with my boot. I went inside for five minutes, came out, and my poor little Americauna is missing a ton of neck feathers and is bloody and exposed. Probably in about an inch by inch patch. I immediately removed her back to the garage because I've heard once they draw blood they won't stop. I locked the Leghorn into the roost part of the coop...but now what? How can I help the injured hen? She's eating and drinking so I think she'll be fine. It just looks terrible. Do I remove the little ones again and put them in the garage? Won't they peck the Americauna now too? Will the Leghorn have a taste for blood and go after all of them now? Clearly, we received bad advice and I feel horrible as it is, so I could really use some good advice now. Who would have thought someone who raised them all his life didn't really know what he was talking about.