Well I have just one male pet duck. And he has been on layer pellets as no where where I live have grower pellets. I have been informed he is lacking niacin by being on layer pellets. I am still trying to get hold of grower pellets online, but in the mean time I am going to sprinkle brewers yeast or get niacin tablets for his water.
Brewer's yeast is a good source of niacin. Niacin is needed when ducklings are growing fast, especially large breeds and ducks that can't free range for insects, etc. Layer pellets are high in calcium and can be hard on a drake and can cause liver or kidney damage. Take a look at storey's guide to ducks for recommendations on home-mixed feed, but you can do a lot with cracked corn, cat kibble, potatoes, free ranging and misc supplements. How old is your drake? What symptoms is he showing?
Most likely if you can get water fowl feed you probably don't need to add extra niacin in the form of brewers yeast or Niacin tab. Most of us can't get it so we have to use feed formulated for chickens, but even then using water fowl man. you may still have a duckling that develops leg issues so then you have to add niacin to their diet. I use an all flock and just for regular maintenance add Brewers yeast [animal] grade to my flocks feed since I have very young and old in my flock. Ducklings can also develop neurological problems from lack of niacin their diet, it usually shows up early in their lives around 2-4 weeks. and can be corrected pretty fast once started on the niacin[b3] they need to be kept on it till 10-12 weeks of age.What is the brewers yeast and niacin for ? What is your feed I use waterfowl maintenance Mazuri