Convulsing hen died. Broken neck?

[jenblossom]

My one year old silkie hen just died. I found her writhing and convulsing. The tightened muscles in her neck caused her neck and head to twist into all sorts of odd (and scary) positions. I have not made any changes in her living environment other than the fact that I added a rooster to the flock one week ago. He grabs the hens by the top of their heads, facing them head to head, rather than mounting them. Could he have broken her neck? They were both bantams. I have two roosters to nine hens. Water is changed every other day. They have a large coop and run. I feed them laying crumbles daily and toss scratch to them every 2 - 3 days. Any ideas?