eggs are a complete source of vitamins for laying hens. I would imagine they would be ideal for young chicks prone to such deficiencies. I wonder if it has to do with the crest because silkies are also prone to vitamin D deficiencies.sfh seem to be especially sensitive to vitamin b deficiencies. medicated chick feed contains amprollium, which is a thiamine blocker.
you might try supplementing their water with liquid vitamins (poly-vi-sol for infants without the added iron works well). some people have found that fermenting their feed also works wonders for the sfh. I've used fermented and regular feed both without issues, but then most of my chicks go out onto grass ASAP, usually under 3 weeks old, and more than likely with a broody, but not always.
I would look first, at the feed you are using. I use the 20% chick crumbles from TSC or the 20% meat bird maker mash from southern states. I've tried higher and lower protein feeds, but not as successfully as with these ones.
many people also supplement their birds with raw chopped liver and other meat sources, if they're not able to free range and hunt for bugs. I do when I find it on sale, but with a dog eating raw, he gets first pick of what's available. (tho when he's not hungry the chickens go nuts over his breakfast).