We purchased a few pullets from a local feed store two weeks ago (Sugar, the oldest and largest (estimated 18 weeks) Rhode Island Red Bantam; Cinnamon (16 weeks, estimated), Rhode Island Red; Honey, the smallest, Australorp). 5 days ago we introduced two new pullets from a local, organic farm. Aside from what we have identified as a leg injury (being treated effectively) in our Australorp, the original three were healthy. The two newest birds are also quite healthy (Ginger, 14 week Golden Comet and Sweet Pea, 16 week Jersey White).
We have slowly integrated the two "flocks" together, originally, Sugar and Cinnamon were picking on Sweet Pea and Ginger. We use a chicken tractor with a moveable fence run and are able to close the door to the coop to separate.
This morning, the fifth day of the integration of the two groups, I was going through my regular pre-leaving-for-work routine when I noticed Cinnamon looking unusual. She had a dizzy look about her and slowly began to twist her neck to the right. She continued twisting until she was on her side on the ground. Breathing seemed to become difficult for her. I lifted her gently and held her. Eventually, she calmed a bit to where she untwisted her neck. I gave her drops of water. After about a half an hour, I set her down. She stood and appeared strong, alert and much better. At this point, she walked over to where Honey was lying and, perhaps 5 minutes from when I set her down, once again twisted her neck and fell in the same fashion.
I ran to find some information. I saw a few articles on wry neck, so I thought I would attempt to give her Vitamin E and selenium. When I returned to the coop, she was twitching on the ground in seemingly much more discomfort. I lifted her out of the coop and sat down with her. She flapped her wings wildly and died.
All of this happened within a two hour time frame.
None of the other birds exhibit any other distressing behavior or concerning appearance (Honey's leg condition has caused her to lay down most of the time, but she eats and drinks very well with support, and as she has been steadily improving, walks more each day and is able to make it to the feeding bowls on her own much more often).
I read about Sudden Death Syndrome in Broiler chickens, but am not certain as to whether this could be the situation.
We decided to bury her immediately, so there will be no necropsy.
If anyone has any insight into what might have caused this, I would be grateful for the input. This is the first flock we have ever raised ourselves from pullets. We work very hard to keep our birds happy, healthy and safe (tractor moves every 48 hours; premium organic feed; fresh water daily; clean food and water bowls every 48 hours; clean roost out once per week).