I have a 3 week old duck that is having issues walking. His legs are bowed and his legs shake when he's just standing still. He tends to lose his balance often. I've had him on Manna Pro duckling starter since he was born. Last week I started giving him Honey Combs Niacin supplement (80mg per dropper) in his water twice a day, along with peas morning and night. I also was pitting brewers yeast in his food with poultry booster. I backed off of the brewers yeast and poultry booster this past week since i started the niacin drops. He's in a large cage but doesn't walk around much. I take him outside for exercise, and swims but I haven't seen any improvement. Any recommendations??