Unfortunately, it is quite difficult to make an accurate diagnosis of what their problem might be over the internet; your best bet would be contacting a veterinary necropsy lab, and sending one of their bodies there for examination, and testing.
https://www.backyardchickens.com/threads/how-to-send-a-bird-for-a-necropsy-pictures.799747/
A good majority of times when multiple birds are being infected there is some sort of an environmental problem, such as moldy feed, rotten carcass, or bacterial infested water contaminating all the birds. It would be good to check over your coop, and pen for anything the birds may be eating or drinking that could cause problems.
Bacterial diseases such as Fowl cholera, caused by the bacterium Pasteurella multocida, can cause discharge from the eyes, lethargy, and often death 6-12 hours after symptoms are first noted. During these times, practice strict hygiene in the coop, ensuring there is no fecal accumulation in the pen or dust that can then spread via airways to other birds. Disinfecting their waterer, and feeders may be a precautious measure as well. Hopefully, you can get this solved.
https://www.merckvetmanual.com/poul...a is a contagious,it can also be asymptomatic.
https://www.backyardchickens.com/threads/how-to-send-a-bird-for-a-necropsy-pictures.799747/
A good majority of times when multiple birds are being infected there is some sort of an environmental problem, such as moldy feed, rotten carcass, or bacterial infested water contaminating all the birds. It would be good to check over your coop, and pen for anything the birds may be eating or drinking that could cause problems.
Bacterial diseases such as Fowl cholera, caused by the bacterium Pasteurella multocida, can cause discharge from the eyes, lethargy, and often death 6-12 hours after symptoms are first noted. During these times, practice strict hygiene in the coop, ensuring there is no fecal accumulation in the pen or dust that can then spread via airways to other birds. Disinfecting their waterer, and feeders may be a precautious measure as well. Hopefully, you can get this solved.
https://www.merckvetmanual.com/poul...a is a contagious,it can also be asymptomatic.