Unknown chicken deaths

[andrewdavis12]

A couple of weeks ago, I found a few of my chickens dead in the pen. Thought it was strange, but not out of realm of possibility. Over the next week, I lost 4 more birds. Now I am very concerned. There are no outward signs of any sickness. I know most of the birds were healthy and died for no apparent reason. I put some antibiotic in their water and was good for a week. Then, I went out last night and found two more in the coop. I am baffled. It is not effecting my ducks or turkeys. Just the chickens. Any ideas and remedies? I don't want o lose any more.

Thank you