I use Vit B Complex injectable in the 100 ml bottle (brand name is Durvet) that I get from the farm supply store per my vet. It's not specifically for poultry, but it still works. I give it orally at the dose of .5 cc per gallon of water for any ducks with issues (1 cc for those really bad, and isolate the bird or birds in question) and making sure that's their only water source for the day. Make it fresh every day, and just pour out the old in the grass/weeds...it won't hurt anything. Since it's water soluble, I don't have to worry about it creating an overdose over time.