so do you have any idea why Damerow in the Chicken Health Handbook p.221 says only that it's caused by a recessive gene, and she does not recommend any treatment?
Does she have a source for that listed anywhere in the book? Looking up the book itself, it's from 1994 and Gail Damerow has been raising chickens for 50 years. Is she a vet? Did she get that advice from a vet? Is there genetics that she's studied and has source material for that?