Ducklings should not be on medicated feed based on my research- I have always started them on non medicated feed.
@Miss Lydia
@Eggcessive
@New duck mommy 2021 - can you back me up on this?
And. Nutritional yeast is a great Niacin supplement - but you may need something more potent to get the lil dude that is struggling back up to speed.
I’ve had good success w Durvet Vitamin B (liquid, injectable for cattle) supplement, available at most feed stores.
You need a syringe (w a needle) to draw it up from the bottle, and then it is squirted over some dry mealworms or soldier fly larvae to encourage them to get the full dose (no injection for the ducky application

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You may need to separate that baby when giving the supplement to be certain that s/he gets it all.
Swim therapy can also help, if it is warm enough where you are.
Separate the little one, offer some supervised pool time, then give the “treats” would be my recommendation, if possible- and 2x daily. You will need to continue treatment about a week after s/he begins walking normally again.
How much does this baby weigh, so we can get you the correct dose?
(A guess is ok.... but a week old Khaki Campbell is a different “bear” than a 6 week old pekin

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