Wow I swear there are alot of posts with these same symptoms...I have been hearing of alot of MG cases and I seriously believe thats what everyones birds is getting...
Honestly the only way to know for sure what your birds have is to get them tested by state vet and find out...Respitory disease may not be fatal but the birds become carriers for life and any birds they come in contact with are likely to get sick as well.... If you go from one cage to another to feed and water your birds they all probably have it as you're probably touching the sick birds and stepping in their feces or collecting their dander on your clothes then messing with the unsymptomized chicks/cornishes...So its probably best to assume all your flock has had contact with the disease. Honestly at this point my best advice would be to cull any symptomatic chickens for now, and cull any future ones that crop up...Do not introduce any new birds into your flock. If you cull any birds take the bodies to be tested by the state vet for disease.
Pale color, watery eyes, runny nose, sneezing, choking/gagging sounds/motions (stretched neck gaping mouth - honking, coughing, or choking sounds) are signs of MG or Mycoplasma but could be one of the other respitory diseases.....these diseases carry from chicken to egg to chick and can be airborne when the chickens go into moult and shed feathers and dander like crazy...Which is this time of year so I warn you again to assume each and every bird in your care/yard is quite possibly infected. But again I suggest culling as symptoms appear if you want to get back to a healthy flock...some of your birds may have a stronger immune system and natural immunity to whats going around in your flock, and if you want to give them a chance i'd suggest culling birds as they appear to be sick, and remove all birds from a house/area to santize it with a dilute bleach solution, a thorough scrubbing, raking the top soil from the ground up and putting down DE and a couple inches of sand in the run area and your usual bedding in the coop/house area...You may be able to selectively eradicate the disease this way from your flock without culling them all.
Good luck and I hope things turn out okay.
