Couple things come to mind.
If you are feeding anything else (fruit, veggies, greens...) in addition to the layer feed, maybe the total protein is not enough. Maybe try a 20% layer feed.
Maybe the dusting every 2-4 weeks is too much handling/stress?
Try putting golf balls in the nest and see if laying doesn't pick-up.
How long since they have laid? Is anything different? New location? New hens/roo's? Construction going on? Anything that may cause stress?
If you are feeding anything else (fruit, veggies, greens...) in addition to the layer feed, maybe the total protein is not enough. Maybe try a 20% layer feed.
Maybe the dusting every 2-4 weeks is too much handling/stress?
Try putting golf balls in the nest and see if laying doesn't pick-up.
How long since they have laid? Is anything different? New location? New hens/roo's? Construction going on? Anything that may cause stress?