I have had chickens for a long time and haven't had any problems. Until two days ago one of my chickens were acting drunk and couldn't walk and just a few hours later was deceased. Then the next day I walk out to my chicken coop and a big rhode island red hen that I was very proud of had like a heart attack then fell over dead. She was just laying on the ground with no movement in her head but flapping her wings wildly. Then two seconds later she was dead. Does anyone have any advice. I haven't introduced new feed or new chickens in 3-4 months.