Baby vitamins is what poly vi sol is. But if you can get the Rooster Booster poultry cell I'd go with it. Order if you have too I have to order everything I need here for my poultry.
In the mean time use the vit E and scramble an egg. prick the E and squirt it on the egg after scremabling. My...
Can you get the polyvisol with out iron? some vitamin E 400iu and scrambled egg for selenium? Plus I believe thiamine is another one this duckling may be missing. are you using poultry cell? it may have thiamine in it.
I'd get this https://jedds.com/products/poultry-cell-rooster-booster make...
Can you post a picture ? here is info on wry neck and treatment.
How's the legs and feet?
https://www.backyardchickens.com/articles/wry-neck-causes-treatment-and-prevention.67732/
You could try making shoes but getting the toes straight might be a problem but worth trying, here is info. https://www.backyardchickens.com/articles/fixing-curled-toes-with-tape-picture-tutorial-and-video.75247/ I know your duckling's toes aren't this bad but using this method may help.
Oh gosh I read that as May sorry. Yes there are doses for very young too. Make sure what niacin you give isn’t flush free or time released. Actually when one has a problem already the liquid b is the best for recovery.
Are you giving any niacin supplements? I think you should try liquid B complex and see if that helps. So since he is a month old 1ml over a tasty small amount of treat daily until he is walking normal.Then another week or 2 after.
Here is some info and what to buy...