Good question, I checked against the vitamins I give and I was wrong for recommending a b complex.
The way you are giving the drug (Niacin) is correct, as Niacin alone is indicated to be used for a dietary supplement like you are giving it daily as a supplement. The B-complex powder I use contains 1% niacin, and the dose is indicated for only 3 to 5 days, so a B complex would not be suitable to give everyday as a supplement, even though some of the individual ingredients may be safe everyday. So my recommendation was wrong about using a B complex everyday. Since you asked I checked and it makes sense, there are about a dozen other vitamins and minerals in a complex and not all of them can be given a long time. I only give it about once a month to the flock.
But just to check the math and recap, the B complex that contains 1% Niacin indicates 2g / gallon, or 0.0005 g/mL, which is 0.00001 g Niacin / mL.
Assuming 100 mL per day per duckling, the B complex I give supplies 1mg of Niacin, which is exactly the target dose, so the assumptions above are all correct. At 2 scoops, you are well within the safe 1mg to 6mg per day range (4 mg / 100 mL).
A b-complex, unlike Niacin alone, is not indicated for daily use, so better to stick with the niacin alone.
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