A lack of calcium, an imbalance in diet and aggression from other hens are the three leading causes of soft-shelled eggs in hens. Some less-common causes of soft-shelled eggs include parasites, diseases and inadequate genetics.
Calcium carbonate crystals make up 95 to 97 percent of an eggshell. Obviously, this implies that a high amount of calcium is important to the development of a healthy eggshell. Hens also routinely lose calcium supplies with the production of eggs on a regular basis, so it is important to supplement or supply hens with a good amount of calcium, either by feeding them their own baked and crushed eggshells or other sources, such as crushed oyster shells.
Chicken layer feed is properly formulated to contain a healthy balance of protein and calcium. However, hens can also be fed treats, such as leftover human food. Allowing treats to comprise more than 20 to 25 percent of a hen's diet can lead to a dietary imbalance.
Henpecking can cause an enormous amount of stress on a subordinate or submissive hen, leading to egg-laying issues. Some hens stop laying eggs altogether. While it is often recommended to allow chickens to determine a pecking order naturally on their own, human intervention may be appropriate if the pecking has become excessively violent or aggressive.