To kabhyper1 - I've never raised chicks under hens as we aren't zoned for more than 5 hens & no roos. There are so many factors to consider in raising babies. They are so delicate. We raised a baby in the house w/ all the care, cleanliness, warmth & socialization you can give 1 chick & still lost her at 19 days old to a violent unexpected seizure in our arms. We raised 2-mo chicks/juvies w/ no problem in-house, but she was our only chick experiment & it traumatized us. Don't know if we'll chance babies again.
It makes sense that chicks would get a lot of dust-ingestion breathing & nesting under a Silkie momma's fluff. I've seen how much dust flies out of a Silkie when she flaps wings after a dust-bath so makes perfect sense. Also I wonder about all the poop that accumulates in sand, straw, chips, shreds, dirt, cat litter, linoleum, concrete, etc, at the bottom of coops. After housing our first 2 Silkies in a coop for their first 2 weeks, we didn't like them stepping in the floor crud - even if it's cleaned daily one watery poop gets stepped in & I didn't feel comfortable about it. That's when we monitored free-ranging the backyard. The little buggers were so surprisingly hardy, cleaner, & healthy, that they've never been cooped all day since. They have a couple low-rise yard shelters to hide or snooze under. They've dug holes to China to the point you can't even see their heads above the dust-baths but they seem healthy & happy in the natural environment. It's amazing in this routine that the nestboxes actually have been staying cleaner too considering it's where they prefer to sleep at night (BYC Post #43184 coop boxes).
As for using poultry dust, it has never been my choice for our Silkies or LF. As I've previously posted the organic OMRI Poultry Protector liquid sprayed in the coop crevices & directly on the hens per directions has been effective for 3 years for us. A bit costly but I don't know how much safer you can get than organic OMRI classified products. I save actual pesticides as a last resort and so far haven't needed to use them in 3 yrs. Since using Poultry Protector has worked for us so far, I won't upset the apple cart & NOT add extra ingredients to their dust-baths. All the experience & advice on this thread has helped reinforce sound practices & common sense.