For Botulism in Ducks, an added medicine was suggested to me by Denver Wild Bird Info & Rehabilitation when 4 ducks of 5 in our public pond died from the natural botulism toxin caused by letting dead fish float on a pond used by ducks:
Miasm-CF available in some Sprouts and other healthfood stores.
In addition to the epsom salts water 1:4 ratio.
Although Cornell and other websites state that ducks should be treated with Botulism Anti-Toxin for the C Strain,
the state of Florida wouldn't provide to our muscovies since they are not native to Florida. Fish & Wildlife thought anti-toxin might be provided to Canada geese, fyi. None of the North Florida hospitals that treat birds (including UF Gainesville) had access to the anti-toxine.
So the above two treatments, along with getting them to eat small pieces of bread in water are one avenue for this horrible disease. FYI most ducks, once found partly paralyzed with bowing necks don't last 48 hrs without treatment. It depends on how much of the toxified pond material they ate as to whether they have a chance. They need to be on changed wee wee pads and bathed, toweled and blanketed too to keep them warm. I nursed one through only but before I learned of the above medicines. Wishing you the best outcome.