I'm just now having the same problem with a Rhode Island Red rooster. That's how I ended up here, looking for an answer.
I did find this -
http://archive.msstate.edu/dept/poultry/disbact.htm#bot
Excerpts -
Botulism is a disease caused by the ingestion of a toxin produced by the Clostridium botulinum bacterium. All domestic fowl and most wild birds are susceptible to the toxin's effects.
Botulism is not a bacterial infection, but a condition produced by a byproduct of the bacteria's growth. The organism is common in nature and is widely dispersed in soils. Ingestion of the organism is not harmful. It becomes dangerous only when conditions are favorable for its growth and subsequent toxin formation.
Weakness is generally the first sign of the illness and is followed by progressive flaccid paralysis of the legs, wings and neck.
Epsom salts (one pound per 100 birds) may be mixed into feed. Adding a level teaspoonful of Epsom salts in one ounce of water and placing in the crops of sick birds has been beneficial in many instances.
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Lots more info at the site. I've just administered epsom salts, I mixed it in water, pedialyte, and a teaspoon of canned pumpkin. He actually liked this and drank it on his own. I then mixed up a little Ionic-Fizz Magnesium Plus that's full of vitamins and gave that to him too. Time will tell if any of this works.
Mine also has sores on the fronts of his legs where they bend (what would be our knees). He was infested with lice and was dusted a few days ago. I've checked him thoroughly and he no longer has lice. Could be the lice weakened his system making him susceptible to botulism which may have come from algae in his water pan.