I think you were able to get a response from sourland, but in case I remember wrong, it is entirely likely that your duckling needs extra niacin - many do, not all seem affected by low niacin in chick feed.
Anyway, one tablespoon brewer's yeast (not baking yeast, brewer's yeast) per cup of food for the next eight weeks is one way to boost the B vitamins, and that includes niacin.
Or you can add 150 mg plain niacin (not no-flush, not timed release - plain niacin, B3) per gallon of drinking water for the next eight weeks.
Don't do both - one or the other.
Anyway, one tablespoon brewer's yeast (not baking yeast, brewer's yeast) per cup of food for the next eight weeks is one way to boost the B vitamins, and that includes niacin.
Or you can add 150 mg plain niacin (not no-flush, not timed release - plain niacin, B3) per gallon of drinking water for the next eight weeks.
Don't do both - one or the other.