Persistency of eggshell quality

Each egg contains about 2g of calcium (Ca) in the form of calcium carbonate (CaCO3). The Ca needed to form the eggshell is coming from feed (60 – 75 %) and the bone (40 – 25 %). With increasing age of the laying hen, the egg increases in size. As the amount of Ca deposited remains more or less constant over time, eggshell becomes thinner towards the end of the laying period. As Ca cannot be stored in the uterus, eggshell formation depends, among other factors, on sufficient amounts of available Ca in the blood during the period of eggshell formation, as well as on the proper function of Ca-metabolism.

With increasing age, Ca absorption in the gut is reduced, which is related to changes in the activity of enzymes involved in the conversion of vitamin D3 to its metabolically active form 1,25(OH)2D3, that plays a crucial role in Ca metabolism.

Good eggshell quality is important for profitable egg production, as undamaged first-class eggs generate a higher price than second-grade eggs. Due to genetic improvement, laying performance and laying persistency has increased in the last years. However, this improvement cannot be fully exploited if eggshell quality deteriorates. Therefore, it is important that the Ca requirement of the hen for the production of high-quality eggshells is met. This is of special importance with increasing age, as the pathways for Ca metabolism are compromised. Taking these changes into consideration helps the laying hen to fulfil its genetic potential.