Seventy-five layers of 37 weeks old, hens were housed in a completely enclosed, ventilated, conventional caged-layer house in which the lighting program was 16 hours' light: 8 hours dark (16L: 8D). The hens were fed on basal diet free from zinc additive for 3 weeks. The hens were divided into 3 groups at 40 weeks of age. The control group was fed with basal
diet. The second group was fed basal diet containing 0.5 g/kg zinc chelated methionine (Zn-MHA) and the third group was fed over dose (2g Zn-MHA /kg) for 8 weeks. Five blood samples were collected from five hens of each group at the end of experiment. Each blood sample divided into three portions. The 1st part of blood sample was collected with anticoagulant for RBCѕ, Hb, and differential leucocytic count. The 2nd part of blood sample was collected with anticoagulant to estimate antioxidative stress melanoldehyde, glutathione peroxidase, superoxide dismutase and carbonic anhydrase (lipid peroxide, melanolyhehyde (MDA), Glutathione peroxidase (GPx), Superoxide dismutase (SOD) and carbonic anhydrase (CA) respectively) in plasma. The 3rd part of blood sample was collected without anticoagulant for serum separation for measuring ALT, AST and alkaline phosphatase, IgA, calcium, phosphorus, cholesterol, LDL and HDL. The present results revealed non-significant changes in hematological profiles including RBCS count, Hb content, WBCS count and differential leucocytic count. Liver enzymes showed significant decrease in ALT, AST and ALP in group 2, 3. Total protein, albumin, globulin, A/G ratio and Ig A revealed non-significant changes in all groups. Also serum Ca, P and Cholesterol, showed nonsignificant changes in all groups but LDL showed significant decrease in groups 2, 3, HDL showed significant increase in groups 2, 3 Vit A level showed significant increase in groups 2 and,3. In the same table oxidative enzymes revealed non-significant changes in MDA (melanolyhehyde) level but there were significant increase in GPx and SOD in groups 2, 3
Exterior egg quality including Egg weight, Egg width, Egg length, Egg index, Shell weight, Shell thickness, Shell percentage showed non-significant changes except egg width revealed significant increase in group 2. Interior egg quality including Yolk weight, Yolk width, Yolk, Yolk index, Albumen weight, Albumen height, and Albumen width showed non-significant changes but yolk height and albumen percentage revealed significant increase in group 3. in the other hand yolk percentage and yolk cholesterol revealed significant decrease in group 3 and in groups 2,3 respectively. Weekly egg production showed significant increase in group 2 from the 2nd week till the end of treatment but group 3 showed significant increases
from the 1st week to the 7th week then decrease in the 8th week. In conclusion, trace minerals (Zn) in the form of Zn-MHA chelates showed higher bioavailability and beneficial effects in compared with inorganic form when included in laying hens' diet