Hi, I had a hen get progressively paralyzed over the course of three or four days and then die. Any idea what caused it? She first started out sitting down and limping a little. The next day she seemed to not be able to stand though she could make her way around a little. The third day, I think, she couldn't move at all and died. The rest of my flock seems fine. She was 3 years old. Any ideas?