They were growing pretty slow. They haven’t gotten their feathers fully quiet yet but the one who died was growing better then the other one still alive. Another duck in my pen (not from the same store) has her neck going bald it looks also. I’m worried it might be something in the pen? I’m in FL
Can you post a pic of you ducks that are okay. By 5 months old they should be all feathered in. Usually feather loss on the neck is from drakes. But have you ever checked them for parasites?
That begs the question, what was the protein% and calcium% of their feed? Was it an all flock type feed with elevated niacin?