Try putting an iodine block or a piece of Millet in the nest box . Suspend a piece of thick string inside the box.
A large hole in the top of the box covered with glass.
An Anti-Pluck spray may just work.
Take the offending parent away.
Administer a liquid calcium directly into the crop with a crop needle.
If you have to try and remove the egg hold the hen partially immersed in warm water
We use wooden shelters but instead of being open across the whole front they have two ends a top and a front, a hole the same diameter as the nest box hole is drilled in the ends and the front, this acts as a magnet to the chicks and the parents usually feed them through the hole.
Do not be in a hurry to blame the Hen, Some chicks die and are then squashed.
If there is a big difference in the ages of the chicks try and even the size's by fostering / swopping the chicks between boxes
Place a larger pot egg in the nest.
ADDITIVES
Keep them to a minimum . Good chicks are bred they don't come out of a bottle.
FRENCH MOULT.
Don't get excited I have not found the cure, I have found the best way to reduce it is good feeding together with a regular use of VIRCON S, particularly between rounds.
