Hello, I recently got my first duck babies and they are about 9 weeks old this week! I have been giving them Brewer's Yeast every day since I got them and I was wondering how long I need to supplement Niacin in their diet? Will they need it until a certain age or forever? I am new to this and want the very best for my babies so I hope someone can help and give me an answer! I appreciate it very much!