In laying hens, calcium (Ca) is of great importance in the eggshell, which requires for synthesis the deposition of about 2.2 g of Ca in the form of Ca carbonate (CaCO3). As egg production will be repeated daily over a long period (50 to 80 weeks), the hen finally exports huge amounts of body Ca for this purpose. Moreover, as the eggshell synthesis occurs mainly during the dark period, when the digestive tract is empty, an additional Ca reserve is mobilized from its bone with a very rapid bone turnover representing a huge challenge to Ca homeostasis and its underlying regulations. The available knowledge on the subject is presented and discussed in the following manuscript, with reference to applied perspectives for the egg producing sector.

Michel Duclos is Research Director (1st class) at INRAE (previously INRA where he led the Avian Research Unit (Unité de Recherches Avicoles) from 2008 to 2016. He is presently Senior Scientist in this unit, now called Avian Biology and Poultry Research (BOA), and is the Vice President of the French branch of the World Poultry Science Association.