I need help. It all started by a hen every so often but the last 5 months I have had about 6 die and I don't know why. The last hen that died today is the only one that showed any symptoms. She was just slow drowsy and when you touched you she fell over she was very weak and now she has died and has brown liquid coming from her mouth and white paste on her butt. But the other hens has shown no symptoms. I check on them at night and then the next day there dead. Help what could it be?