The symptoms suggest Marek's, but I am confused by the randomness, and the fact that it only strikes my Polish. I also have Silkies, Orpington's and Serama's, and have never had any of those show these symptoms, and they are often penned together for grow out. The symptoms I have are: 1. Hits suddenly between 3-5 months of age. 2. Wobbly legs, progressing to walking backward, and eventually paralysis with one leg shooting straight forward, or backward. 3. Dropping wing, and flapping to maintain an upright position. With each occurrence I have tried anything I could find on the internet, from antibiotics to supplements. I even thought it may just be head injuries from fighting, since Polish do have a soft spot on their head. But the latest bird is all by himself in a grow out cage, because I was trying to protect him from that. He is 5 months old. Last night he was perfectly fine. This morning he is wobbling and drooping a wing. If I can get him up on his feet, he goes backwards. Even with hand feeding and watering, I have never had one bird recover, or even survive, from this. Is it Marek's, or something else. Even genetics would be confusing, since I have 3 small flocks with completely different bloodlines, and get this in youngsters from all 3 pens.