when you said drop in egg production I wondered about mites and lice. It is hard from your pics, but the little grey puffs at the base of the feathers look like they could be lice eggs to me. Are they kind of stuck to the feather shaft?
When chickens are ill, they are more susceptible to lice/mites...
It wouldn't hurt to dust them, very best is with wood ash but second best, in my mind, is the flower poultry dust you can get at the feed stores.
I think Minniechickmama has some earlier posts about ivermectin or something like that to treat mites/lice too, there is probably egg withdrawal with that.
I had a problem earlier this winter and just dusted the birds, but a couple months later I'm back at it. I did not clean the coop out which is generally recommended with lice/mites (because it was the dead of winter and usually just dusting them is sufficient). I am going to empty the danged thing and do an early spring cleaning, weather permitting, in the next couple of days, before I have to do the second round of dusting (once for the critters, once later for eggs/hatchlings).
edited to add: oh yeah, I do think that is feather damage from roosters that you are seeing, but the grey lollipops at the base of the feathers is different.
no fun!
