HOUSING SYSTEMS BIOSECURITY HOUSING & BROODING EARLY MANAGEMENT LIGHTING NUTRITION HEALTH HATCHING EGG MANAGEMENT 71 71 LOHMANN › MANAGEMENT GUIDE TILL 30 WEEKS: END OF PREPARATION PERIOD MEDULLARY BONES Structural bone development continues until weeks 15–16, after which production begins, depending on the lighting programme. From this moment, a hormonal change (oestrogens) occurs, leading to the development of the reproductive system and a particular type of bone called “medullary” (mainly in the tibia and femur) while the demand for nutrients for growth continues. During lay, the formation/calcification of the eggshell takes place during the dark period when feed/calcium is not available. It is then when the hen mobilises (resorption) between 25–30% of the calcium requirement from the medullary bone to meet the demands for shell formation. Coarse carbonate/oyster shell (> 2 mm ø) is retained in the gizzard and, through the action of hydrochloric acid, dissolves, providing a flow of calcium to the intestine during the night when no feed is available. Ca Ca Ca FORMATION OF THE EGGSHELL DURING THE DARK PERIOD, FEED CALCIUM IS NOT AVAILABLE 60–70% CALCIUM FROM CROP & GIZZARD 20–30% CALCIUM FROM MEDULLARY BONE THE HEN LAYS AN EGG SHORTLY AFTER THE LIGHTS ARE SWITCHED ON REPLENISHING THE CALCIUM IN THE BONES THROUGH THE MORNING FEED 1–1.5 HOURS BEFORE LIGHTS OFF: STORING AS MUCH CALCIUM AS POSSIBLE IN THE CROP AND GIZZARD THROUGH THE EVENING FEED This process emphasises the importance of good bone / skeletal development. The growth of the calcium warehouse.
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