those 18%-20% or higher feeds will do it every time.
I disagree. It has more to do with carbohydrate content and mineral/vitamin deficiency.
"When a young bird eats
calorie-dense, nutritionally poor foods like bread the growth of its feathers outpaces the development of its wing bones. Gravity pulls the heavy feathers down, and the growing bones twist outward, resulting in a syndrome known as Angel Wing. Bandages and physical therapy can correct the condition in young birds, but it is incurable in adults, and affected birds lose the ability to fly."
http://www.spokanecity.org/services/articles/?ArticleID=1850
I feed high protein game bird feed to all my birds. Cases of angel wing? ZERO. I am on a 3rd generation of ducks raised on high protein feed. I also supplement with greens (dandelions, clover, lettuce, peas, cabbage, etc...) and high protein natural foods like duckweed, worms, fish, etc...
Study the diet of a duckling in the wild. What does it eat? Water plants (like duckweed, which is high protein), worms (high protein), insect larvae (high protein), and some plants. What a wild duckling does NOT eat is corn and soy. So how protein, something they evolved to eat in large quantities as ducklings over millions of years, got blamed for angel wing is beyond me.
P.S. Flock Raiser has caused issues for people here including angel wing, leg weakness and pin holes in foot webbing. I adopted ducks from someone who fed flock raiser and the ducks had all kinds of tiny holes in their feet. 1 week on game bird feed (24% protein) and they healed right up.