This maybe a long term treatment with your duckling. Pekins grow super fast and their legs just have a hard time keeping up. I use Nutritional yeast everyday for myself it’s packed with B vitamins so once your little one is up and going good you can switch over to Nutritional yeast. My flock still get it in their feed and my ducklings are getting it everyday in their starter. But you want to start with the liquid b complex when one is already having trouble. The NY will be 1 Tab per each cup of feed you use.