I am treating acute severe niacin deficiency in a pekin drake. I find that the Durvet High Level Vitamin B Complex is a little oily and takes time to soak into dried mealworms. So I put a little brewer's yeast in there too and it helps the absorption. Something must smell good as my other ducks...
Add 1 tablespoon of brewer's yeast to each cupfull of pellets. Egg laying female ducks often need more niacin than in Flock Raiser.
Brewer's yeast can clump if mixed in a big tub. I find it best to sprinkle the yeast over the pellets in the feed bowl, My ducks love the yeast on the top.