i read this thread last night before bed and woke up with some thoughts. Apologies if this was covered elsewhere, but I may have missed pages. 163! Whew!
So, genetically speaking, could this be a mutation in the growth/development? Perhaps something switching in the down also affects the maturation? It seems like fatalities arise near eggbearing/crowing, so could it be some issue with stunted growth? Does the down without pins affect warmth? Maybe they have temp regulation issues and don't roost together?
Some thoughts on roo on hen issues: I know there are some species that have built in "relative" detectors and will not breed with siblings because of the risk of mutations. Especially with a hen refusing a mate. She may sense that ill breeding is afoot. Or maybe the silkie feathers we all love and strive for are a sign of non-hearty offspring? Are the roos breeding well with others? How are those hatches doing? This is all very interesting! If the breeding is done responsibly (as it seems is happening) these may rise the ranks to stardom quickly.
So... how are the projects? I'm not able to breed (I am innkeeper and roosters would no doubt disturb some guests) but anyone culling hens should let me know! We have a pretty temperate winter here and I just think these birds are lovely!