I have a flock of now 18 Sebrights and a couple days ago I went out to let them out and three hens were dead for what must have been awhile they were stiff when I took care of them. It was one of our colder nights that we have had also. The hens were not mutilated but one of them had it's insides out it's bottom. This morning I went out and I have another dead hen outside without any mutilation and last night was very mild weather wise. They do have a vent in the coop that they will sometimes let themselves out of in the morning if they want to get out before I open them up. I just find it strange that it is only hens that are dieing on me and I really have no idea what is killing them. They were born the last week of June and are just reaching maturity. Ten hens with eight roosters I also have another flock of standard size chickens but they are kept in seperate coops. Any idea's of what I may be looking at as the problem? I am really at a loss as to what is happening. I do have two dogs that enjoy terrorizing the chicks but I know there is no possible way they could have gotten to the first hree hens that died and I just find it perplexing that it has been four straight hens and no roosters. Thanks for any help.