Amprolium was an issue, a serious issue actually, for me at one time because in addition to my hens, I also got two geese.
I spoke with the Purina people and they were vague. Then I ran across geese and duck people who have fed their birds feed containing amprolium from the get-go. Then a University guy said that's all they feed their geese and ducks and have never had any problems. However, bill deformaties have been reported somewhere at sometime, but darned if the research isn't available.
Amprolium is in chick starter crumbles. Those crumbles, I also discovered, are recommended for ducks and geese by some authorities.
So, it's a confusing mess of contradictions.
The greater harm to our birds, in my opinion, would likely come from contamination of feed components that were made in foreign countries.
I don't feed straight crumbles to my goose. I mix it in with the corn. My goose likes the crumbles. The hens, however, hate it.