10 ducklings from tractor supply not going so well

[Borgia]

I bought 10 ducklings from tractor supply within about 5 days 6 were dead. Over the next week the others would die too. I'm down to one who I think will be gone soon. I'm trying to figure out what the problem is. Whether it is just a bad batch or something I am doing. I have the light, water and have been feeding mannapro made for ducklings. One thing I have noticed is problems with legs which seems like niacin shortage. Before they die they go bo legged and flip and get stuck on their backs. The mannapro says it has all supplements needed. Today I started giving the last duckling niacin directly. Anyone have any ideas? I've raised ducks before no problems. Tractor supply is replacing the original six that died and I want them to survive.

 

[Isaac 0]

Sounds like a B3 deficiency, they have cattle injectable vitamin B at most feed stores can you get some for the last duckling? It looks like this. 1ml a day till he gets better.