Get rid of the hay. It has mold spores. Just put a blanket it there. I would also add Apple cider vinegar to the water. You also need a probiotic in the feed with some copper to regulate the gut flora. A little plain yogurt. Sounds like a bacterial or yeast infection. Is the comb purplish?
Sounds like a toxin in your soil. What's on the ground? Fertilizer.? For them to die that quick sounds like a neurotoxin. Are you spraying for pests? Sevin?
I believe my hen has this as she has a white gooey discharge coming out of her but. I read about it and it is caused by Candida which is a FUNGAL infection. Antibiotics do not work for fungus. The Epsom salt bath is strictly for comfort and healing the infected skin area and keeping down any...