Effect of 25-Hydroxycholecalciferol with Different Vitamin D₃ Levels in the Hens Diet in the Rearing Period on Growth Performance, Bone Quality, Egg Production, and Eggshell Quality

A study was conducted to evaluate the effect of 25-hydroxyvitamin D₃ (25-OHD) with different levels of vitamin D₃ (VD₃) during the rearing period (1–20 weeks) on laying hen performance, bone quality, and eggshell quality. A total of four hundred 1-day-old Lohman pullets were randomly allotted into a 2 × 2 factorial design with 2 levels of dietary VD₃ (300 and 2800 IU/kg) and 2 levels of dietary 25-OHD (0 and 56 μg/kg). Each treatment had five replicates of 20 hens each. Increasing the dietary VD₃ level (2800 vs. 300 IU/kg) tended to increase body weight uniformity (0.05 < <i>p</i> < 0.1) at 8 weeks. Dietary VD₃ levels and supplementation of 25-OHD during the growing period (1–20 weeks) did not improve the laying performance and eggshell quality (eggshell strength, eggshell thickness, and eggshell relative weight) during the laying period (<i>p</i> > 0.05). Compared with the 300 IU/kg VD₃ group, the 2800 IU/kg VD₃ group showed higher serum calcium concentration and keel length at 10 weeks (<i>p</i> < 0.05). The addition of 25-OHD significantly increased serum calcium and 25-OHD concentration at 10 and 20 weeks and keel calcified rate at 20 weeks (<i>p</i> < 0.05). Increasing dietary VD₃ level (2800 vs. 300 IU/kg) increased tibia ash and phosphorus content at 10 weeks, tibia strength at 72 weeks (<i>p</i> < 0.05), and tended to increase tibia ash content at 72 weeks, tibia calcium content and tibia strength at 20 weeks (0.05 < <i>p</i> < 0.1). Dietary supplementation with 25-OHD increased tibia ash content at 10 weeks, tibia calcium content and tibia strength at 20 weeks (<i>p</i> < 0.05), and tended to increase tibia ash content at 72 weeks (0.05 < <i>p</i> < 0.1). Overall, the results gathered in this study indicate that dietary supplementation of high levels of VD₃ and 25-OHD during the growing period improved the tibia quality of laying hens during the early and later laying period, but had no effect on laying performance and eggshell quality during the laying period.