Calcium is the primary mineral that makes up eggshells and when not supplied in the diet, the hen does not have the basic materials needed to make the shell. The problem is produced when whole grains or feeds deficient in minerals and vitamins make up the bulk of the laying hen diet. Thin egg shells are observed when calcium, phosphorus and vitamin D3 are not provided in diets at adequate levels. It is more often observed during periods of hot weather because calcium is conserved and retained within the hen's body less efficiently.

The quality of the shells is improved by feeding a complete laying ration as the only diet. This diet supplies all nutrients in the proper proportions so the hen can produce good shells. If thin egg shells becomes a problem, it is advisable to add 2 pounds of oyster shells (as an oyster shell flour or hen-sized oyster shells) to every 100 pounds of complete layer ration.

This will provide a quick remedy to the problem and should restore egg shell quality within a short period of time. After the egg shell quality is restored, the addition of oyster shell can be eliminated and the complete layer diet can then maintain good egg shell formation. It is also advisable to also add a vitamin supplement to the drinking water while the oyster shell is being added to the feed. This will help ensure that calcium and phosphorus in the diet is being properly absorbed through the digestive system and will be available for deposition as shell on the egg.