Plasma estrogen was increased considerably with VD 3 supplementation at 3.5% Ca, but parathyroid hormone levels were not affected. Increasing the Ca level caused a stepwise increase in catalase, which was markedly increased with VD 3 supplementation at 1,200 IU. Increasing the Ca level to 4% significantly reduced serum triglycerides, and the very low-density lipoprotein and the triglyceride/high-density lipoprotein ratio were both decreased with 4 and 4.5% Ca level diets. VD 3 addition at 1,200 IU to the 4% Ca diet significantly increased γ-globulin compared to 1,000 IU, but decreased β-globulin. Increasing Ca level increased IgA, and 4 and 4.5% Ca levels similarly increased IgG and α-2 globulin compared to the 3.5% Ca diet. In addition, VD 3 at 1,000 IU increased serum albumin, compared to 800 IU. Increasing the Ca concentration from 3.5 to 4 and 4.5% and increasing VD 3 levels from 800 to 1,000 or 1,200 IU significantly and similarly increased serum total protein and globulin. Similar results were observed in eggshell quality measurements and tibia ash. Besides this, the addition of VD 3 at 800 and 1,200 IU to 3.5% Ca level diets enhanced the Haugh unit score. The addition of VD 3 at 1,000 and 1,200 IU to 3.5 and 4% Ca diets significantly ( P ≤ 0.05) increased the rate of laying, egg mass, and feed conversion ratio (FCR) compared to the control diet on 3.5% and 800 U of VD 3. The control diet in this experiment contained a 3.5% Ca level with 800 IU VD 3. Three hundred and sixty H&N Brown egg layers (60 weeks old) were allocated at random into nine nutritional treatments of five replications (cages) of eight hens each. The influence of Ca levels (3.5, 4.0, and 4.5%) and/or cholecalciferol supplementation (800-, 1,000-, and 1,200-IU/kg diet or as total of 3,800, 4,000, and 4,200 IC VD 3) on performance, egg quality, blood biochemistry, and immunity of brown egg layers was investigated. Productive traits and immunity in laying hens decrease sharply during the late phase of laying due to aging, which negatively affects the metabolism and hormonal status of the animals. 2Poultry Production Department, Faculty of Agriculture, Mansoura University, Mansoura, Egypt.1Department of Agriculture, Faculty of Environmental Sciences, King Abdulaziz University, Jeddah, Saudi Arabia.
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