I also have this problem. I have 4 Pekin ducklings that are 3 weeks old on Monday. 3 of them are doing just fine but one has a bald spot that I supsect was from getting pecked at. But I watched them and they all get along now. One does have a limping problem and walks quite oddly. The others follow me sometimes and when they do, he comes with but is always at the end of the pack. He can get to his food and water fine but it is plainly obvious that he is having trouble moving. He stays sitting down more than the others as well. I just got Brewers yeast tonight and will mix into his food separately so he gets some for sure. But I also don't know how much to put in. Any suggestions on proportion or other possible reasons he's doing thing? I really think it's niacin deficieny but it could be something else... They've all been swimming twice so far, so should I let them swim more? I just don't want the poor guy to suffer.