If I were you, I would either take one of my birds to the vet for a blood test OR sacrifice one of my birds and send it in for a necropsy to get a definite diagnosis. Your poultry guy could certainly be right, but I'd rather cull one bird and find out what it is in the hope it's treatable, rather than destroy my entire flock with a best guess.
Either way, it's awful, and I'm sorry you're having to go through this.
You can contact your local vet or the local college/university agriculture department to get information on where to send for a necropsy. If you have a bird that passes or one that you cull, place its body in the fridge wrapped in plastic bags (NOT the freezer), and ship it to have the necropsy done.
The necropsy is most likely free, but you'll have to pay for shipping if you go that route.
With a diagnosis, you can formulate a plan and know for sure what to do.
MrsB
