It’s rec they have supplemental niacin till age 10 weeks old. I usually start my ducklings off on Nutritional yeast and keep the liquid b complex for any issues that come up. My last hatched duckling used the liquid b complex right out of the shell daily until 10 weeks. If one of yours begins to have leg weakness or shaky leg then you can dose that one separate from the others orally but that hopefully won’t be needed.