The thickness of an egg shell is determined by the size of the egg. A hen produces a consistent amount of shell material for each egg she lays. Smaller eggs tend to have thicker shells, while as the hen ages and egg size increases, the shell becomes thinner.
If a hen isn’t getting enough calcium through her diet, the necessary calcium for the shell will be sourced from her body. That’s why farmers provide hens with a calcium-enriched diet.
Learn more from Ontario egg farmer Hubert.