[susiesmith]

A couple of weeks ago I noticed I had a chicken with a droopy tail and she was lethargic, unfortunately she died a week later, I have now noticed another chicken behaving in the same way, I am going to separate her from the others and give her some antibiotics, any ideas what the problem might be?

[joyfull]

not without seeing the bird - I suggest you take her to a vets, 

[ANHBUC]

I second what joyfull says.

If you are giving antibiotics it might have an affect on what the vet prescribes.