As a layer flock ages the quality of their eggshells decline and the percentage of cracks increases. Also, the relative number of eggs with heavily spotted shells increases with age of a layer flock. Research has shown that as the hen ages the egg gets bigger and the shell becomes thinner. Simply, the size of the egg increases and the amount of shell deposition remains somewhat constant and, therefore, the shell thins. The calcite columns in the palisade layer of the shell become shorter with hen age and research in eggshell quality has shown that fracture strength of the eggshell is directly related to the thickness of the palisade layer. In older flocks, the combination of increased spotting and thinner shells has a cumulative negative effect on egg breakage as well as moisture loss. The increased moisture loss has a negative effect on hatchability.
Egg hatchability can be decreased by 3 percent to 14 percent when spotting of the eggshell is high, especially in older breeder flocks. The decline in eggshell quality in older flocks is also highly correlated with an increased bacterial penetration of the eggshell. Minimizing the number of stressors and their intensity in the environment of commercial egg-type hens and breeders will keep the stress level low in the birds and this is usually associated with a decrease in the amount of eggshell spotting/mottling, especially in older flocks.
