HI,
I have experienced the same symptoms with my new chicks. And have now lost 5 of my 29. I tried probiotics and electrolytes and additional vitamins thinking it was a deficiency of some kind. All with no results. I have sanitized the coop, I clean and clean, even power washed. Found the same article about botulism and figured that is the best fit. But I can't imagine what they would be getting into that is dead and decaying. I'm trying antibiotics now which means no probiotics for the moment so I'm supplementing with liquid vitamins. Any luck with yours?