Hens are 1-year-old Rhodeys, seem healthy except for feather loss on head, neck and vent area. Two have died in the last week. Both were laying until they died. Checked for mites/lice and can't see any. An on-line vet suggested Duramycin and I am starting a course of that although I'm not sure that will be the answer. Have watched and there is no pecking going on. Any help would be appreciated.