We have 3 week old ducklings and one of them isn't walking like the rest of them. He can hardly stand up and when he does have to walk he has a really hard time and it looks like he's drunk, staggering all around. Most of the time he is just sitting while all the other ducks are moving around. He is also a lot smaller than the rest of them. I've read a lot about Niacin deficiency in ducks so I have been adding brewers yeast to the ducks food only for a few days now. I guess I'm just wondering if it's possible for only 1 duckling to have a niacin deficiency. And if this is what it sounds like is wrong with my duckling.