A cough that won't quit!

I have a huge variety of chickens, young and old. Everything was fine, they were picking my property clean of bugs, laying eggs, and giving me hours of entertainment before I brought home 4 ostralop pullets to add to my eggs. They all seemed healthy at first, and the guy said that they were all vaccinated and wormed when I bought them. That struck me as odd because I have never had to give my chickens anything, but I assumed he knew more than me and it was to keep them healthy for the transition.

After a few weeks I found one laying in my garden alive, but very light and weak. I set up a chicken ICU gave electrolytes and probiotics. The hen died a few days later. Then this happened to two more of them. One survived and is almost a year old, never has laid an egg, but I don't have the heart to kill her.

Suddenly a few weeks ago I found a dead chick in my coop with no explanation. A few days after that I heard a weird cough like the hens that died this summer had. I waited for my babies to come back to the coop for bed and many of them had drippy noses, and raspy breathing. They have been on a high dose of duramyacin for 8 days with no improvement. Their combs and waddles are going pale and I'm only getting one egg a day.

I should mention no more have died, they are eating and drinking more than normal (but it has been cold here and there are less bugs), they have plenty of energy, they have diarrhea, and my chicks are still growing like crazy.


Does anyone know what this is or how to treat it? Has this happened to anyone else before?