Buff Orp vomited clear liquid and died - anyone know why?

[cperezpeeps]

I've had 4 Buff Orps for the past 2 years and lost our first one last night. I'm feeling devastated and don't know what caused her death. She had been hanging out in one of the nesting boxes all afternoon and didn't seem to be laying any eggs. When I saw her in the nesting box this evening while the other hens were still scratching around in the run I went to investigate. I picked her up and she immediately starting vomiting clear liquid. I shifted her in my hands but it continued on and on. Her comb started to turn purple-ish, and she got really distressed. This lasted for a few minutes, with her continuing to vomit clear liquid, flapping her wings, etc., then she died. She looked like she couldn't breathe. I'm worried she has a sickness that is brewing in my three other girls. Any thoughts on what caused this?