Calcium (Ca) is a crucial element for life (Brini et al., 2013) and is required for a number of cellular and molecular mechanisms. It is also the main constituent of the skeleton, being complexed with phosphorus (P) to form hydroxyapatite. Apart from its mechanical properties, the skeleton also acts as a metabolic reserve of Ca, which can be exchanged with the plasmatic pool through bone remodelling. In laying hens, Ca is of great importance in the eggshell, which requires the deposition of about 2.2 g of Ca in the form of Ca carbonate (CaCO3). As egg production is repeated daily over a long period (50-80 weeks), the hen exports up to 50 times its body Ca.