The trace minerals manganese (Mn), zinc (Zn) and copper (Cu) are essential minerals in the diet of laying hens as they are needed for growth; they play an integral role in the immune system, carbohydrate metabolism and protein synthesis. They also have specific functions in the formation of bone and eggshells. Zinc is a cofactor of the enzyme carbonic an- hydrase in the uterus. It catalyzes the condensation of CO2, and H2O, producing H+ and HCO3. The latter combines with calcium, forming calcium carbonate in the eggshell. A lack of zinc in layer diets can lead to lower levels of carbonic anhydrase, resulting in shell defects Copper is an essential element for reproduction, growth, development of connective tissue and skin pigmentation. It is a component of blood proteins such as erythrocuprein that is found in erythrocytes and is active in many enzyme systems. It is also essential for normal bone formation.The lack of copper in laying diets can lead to a high- er incidence of eggs produced with peel malformation. Manganese is a metal activator of glycosyl- transferase and alkaline phosphatase enzymes, which are involved in the synthesis of mucopolysaccharides and glycoproteins that contributes to the formation of the organic matrix of bone and eggshell. A lack of manganese leads to defects that may include less shell mass