So I have a duck that can't walk because her legs are so weak. I have tried everything from niacin pills, brewer's yeast, milk, vitamins, new feed. But I am wondering if the fact that for some reason she seems to still have some yellowy down (along with feathers) on the upper neck and top of her head indicates anything. Maybe that points to something else other than a niacin deficiency. Her brother, same age, long ago lost all his down and is pure white. Has anyone of you ever seen this on your ducks before?