I took a rescue duck on recently she lost all her feathers starting with from around the eye. Like you in 15 years of keeping ducks, I’ve never seen anything like it. It turned out to be a mite living under the skin which eats the feather before it has chance to grow. She was treated with XENO...
I am not going with the niacin deficiency. I would say it’s more likely a worm overload, canker or heavy metal poisoning. Of Course there are lots of other things it could be, but I would start with those first.
