Plain niacin, not flush free or time released, start when 1-4 weeks at 150 mgs into 1 gal of water. crush the tablet or open capsule and mix well. You will most likely have to ask for the plain because for some reason it's kept behind the counter. also you can use Brewers yeast sprinkled on their feed. 1 Tab to 1 cups of feed.What kind of niacin should be given to ducks