dont know what vets you chaps are using? but from what i have just been reading danw knows his onions,use a poultry vet.
caradox is for enteritis all you are doing as a preventitive is stoping the bacterial enteritis which can then lead to hexy.
most game birds carry hexy and coxy and other nasties at acceptable levels that the birds are fine it takes a "trigger" like enteritis or bad gapes or any of the other minor nasties to start the secondary infection i.e. hexy.
99% of birds will die from dehydration as danw says treat with a rehydration at same time like solulyte.