ISSUE FOCUS FEED & ADDITIVE MAGAZINE February 2026 73 of the total egg mass remains relatively constant throughout the laying period as its share is genetically predetermined. Consequently, as the egg is getting larger, the eggshell is getting thinner. Considering the fact that the eggshell consists of 96% calcium carbonate the importance of calcium supply is evident to ensure stable eggshells. With age, shell thickness also decreases, because calcium availability reduces. As a result, the breaking strength of the eggshell declines and more and more eggs show cracks or abnormalities. In the first half of the laying period, the percentage of broken eggs is neglectable, but increases in the second laying period and requires feeding-related or management measures. HOW ACTIVATED VITAMIN D HELPS It is not only the size of the egg that influences the breaking strength of the eggshell. It is also a proper absorption, mobilization and transport of calcium. Vitamin D is an essential molecule which activates calcium transport and influences its absorption rate. Because of the importance of both, a supplementation with vitamin D and calcium should be ensured throughout the whole production period. Unfortunately, it is not always the case, especially in older laying hens, as the function of organs such as liver and kidneys is impaired by environmental influences. The production of specific enzymes involved in the metabolization of vitamin D declines. The availability of calcium in bones also decreases as reserves are depleted. In this case plant based Active D may help as it provides the already activated vitamin D glycosides which are directly available for the hen. Activated vitamin D offers the advantage that it does not require the vitamin D metabolic pathway and is therefore not dependent on enzymes or organs functionality. As a result, the mobilization of calcium from the feed is maintained in critical phases and more calcium is available for the formation of the eggshell. A field study conducted by the University of Sydney and described below shows the positive effect of Active D in old hens. USE OF ACTIVE D IN OLDER BROWN LAYING HENS A total of 240 Hy-Line Brown layer hens, 55 weeks of age, were purchased from a commercial **** Treatment 2 Control Treatment 1 Shell thickness (mm) 0.50 0.45 0.40 0.35 0.30 64 68 76 80 85 Weeks of age P = 0.067 - 0.074 The use of plant-based Active D, containing activated vitamin D led to a significant higher eggshell thickness after 85 weeks of production. Eggshell Quality – Shell thickness
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