[B]@Isaac 0 need to add?[/B]
The only thing I would add is, to gently exercise the neck back into place more than several times a day, sometimes ducklings like this didn't stem from a nutritional deficiency, but rather from a malposition during the incubation period which caused there neck to be pulled in such a way.
The good thing is with ducklings this young, if it is a nutritional deficiency you should be able to see improvement within a few hours/ days. If you don't, you need to start considering other problems.