Quatie
Free Ranging
I have the Purina Flock Raiser. I looked up the niacin content of the feed and it's hard to find a number for that. It says guaranteed enough for ducklings but I'm not seeing an actual amount.
So purina contains at least 55 ppm according to the purina expert on TSC. Their article below claims 60 ppm. The minimum for ducklings is 55 ppm. Your feed is fine as is. So the nutritional yeast is just extra.
Hopefully this link works.
https://www.purinamills.com/2.purin...cks-and-Other-Poultry-E-book_FINAL_072319.pdf