Effects of Supplementation of 25-Hydroxyvitamin D3 as a Vitamin D3 Substitute on Performance, Bone Traits, and Egg Quality of Laying Hens from 1 Day to 72 Weeks of Age

This experiment was conducted to explore the effect of long-term supplementation of 25-hydroxyvitamin D3 (25-OHD) as a vitamin D3 (VD3) substitute on performance, bone traits, and egg quality of laying hens from 1 day to 72 weeks of age. In total, 900 one-day-old Lohman pullets were randomly allotted into three dietary groups (three treatments × 15 replicates × 20 birds per replicate): VD3 2800 IU/kg; 25-OHD 69 μg/kg; 25-OHD 125 μg/kg. At the end of the 20th w, five replicates from each group were selected to feed on the same vitamin D diets, as used during the rearing stage (1–20 w) until 72 w. The result showed that the 25-OHD 125 μg/kg treatment had the lowest average daily feed intake (ADFI) at 1–8 or 1–19 w, body weight at 8 w, body weight gain between 1 and 8 w and shank length at 4 w (p < 0.05). The 25-OHD 125 μg/kg treatment had a lower shank length at 7 w, compared with the 25-OHD 69 μg/kg treatment. The shank length of the birds in each treatment reached the maximum (about 103 mm) at about 18 w of age. For the bone traits, the 25-OHD 125 μg/kg treatment had the lowest femur bone diameter at 20 w (p < 0.001) and femur bone plumpness at 20 w (p = 0.002). The 25-OHD 125 μg/kg treatment had a lower tibia strength at 10 w (p = 0.023) and keel length at 10 w (p = 0.046), compared with the 25-OHD 69 μg/kg treatment. However, both 25-OHD 69 and 125 μg/kg treatments had a greater femur strength at 72 w (p = 0.006), compared with the VD3 2800 IU/kg treatment. No difference in laying performance was observed among all treatments. The overall (21–72 w) ADFI in the 25-OHD 125 μg/kg treatment was significantly lower than that in the 25-OHD 69 μg/kg treatment (p = 0.030). At 60 w, the 25-OHD 125 μg/kg treatment had a lower eggshell thickness (p = 0.012) and proportion of eggshell (p = 0.022), compared with the 25-OHD 69 μg/kg treatment. No significant differences in egg quality parameters were observed at 50 and 70 w among treatments. In general, supplementary 2800 IU/kg doses of VD3 at the early stage were sufficient to maintain the bone quality and growth and development of pullets. Feeding birds at a higher 25-OHD level (125 μg/kg) resulted in the reduced ADFI and growth at the rearing period, but the long-term supplementation of 25-OHD as a VD3 substitute improved the bone quality in the late laying period.