This experiment was conducted to study the effect of supplementing layer diets with two vitamin D (VD) sources included three levels from each of vitamin D₃ (VD₃) and 25-hydroxycholecalciferol (25-OHD₃) on egg production and reproduction performance. At 11 month of age 189 layers and 21 cocks were chosen and distributed equally into 9 groups. Each group contained 3 replicates contained 7 hens and 1 cock each. Nine experimental diets were formulated, the first one was control diet that contained 2500 IU VD₃/kg diet. The 2^nd and 3^rd diets formed by supplemented control diet with 1250 and 2500 IU VD₃/kg diet respectively. The previous three diets supplemented with 0.04 mg 25-OHD₃/kg diet to create the 4^th, 5^th and 6^th diets respectively. To perform 7^th, 8^th and 9^th diets the first three diets supplemented with 0.08 mg 25-OHD₃/kg diet respectively. The experiment was extended for four months and egg production performance, reproduction performance and liver enzymes were measured. The following results were obtained:

Supplementation of 25-OHD₃ improved significantly egg production% during the 2^nd month and entire experimental period. Increasing total VD content than NRC (1994) increased significantly (P< 0.05) egg production% than control treatment after the 2^nd month. Hen's persistence showed clear improvement especially with diets contained total VD from 0.125 to 0.17375 mg/kg. Egg mass per hen per day was improved as seem as egg production%.
Feed intake of entire experimental period was increased significantly (P < 0.05) by increasing VD than NRC 1994. Significant improvement (P < 0.05) was observed in feed conversion when diet contained 0.17375 VD mg/kg compared with control treatment. Neither reproduction performance nor liver function influenced significantly by VD source and levels.
We recommend that 25-OHD₃ should combine with VD₃ in layer diets at late stage but not more than 0.17375 mg/kg.