Vitamin D_2 impairs utilization of vitamin D_3 in high-yielding dairy cows in a cross-over supplementation regimen

摘要

Vitamin D exists in 2 forms that are important regarding vitamin D status and supply in cattle: vitamin D_2 (D_2) and vitamin D_3 (D_3). To become physiologically active, both D_2 and D_3 must undergo 25-hydrox-ylation in the liver. The resulting 25-hydroxyvitamin D_2 [25(OH)D_2] and 25-hydroxyvitamin D_3 [25(OH)D_3] are measured as indicators of the physiological vitamin D status of cattle. The study used 14 Danish Holstein cows housed without access to sunlight. The cows were orally administered 250 mg (1.0 x 10~7 IU) of D_2 and D_3 in a cross-over design with 2 treatment groups and 2 study periods, rendering 4 treatments when carryover effects were taken into account: D_2 given first, D_2 given last after D_3, D_3 given first, and D_3 given last after D_2 Two weeks elapsed between the treatment in the first study period and the treatment in the second study period. Blood samples were collected 0, 3, 6, 14, 17, 20, 23, 26, 40, 48, 70, 94, 166, and 214 h after providing the oral bolus of vitamin to the cows. Comparisons between plasma levels of the metabolites D_2, D_3, 25(OH) D_2, and 25(OH)D_3 over time were made by comparing areas under the plasma concentration curves. Oral administration of D3 increased plasma D_3 (182.6 ± 17.1 ng/mL; mean ± SEM) and 25(OH)D_3 (103.5 ± 10.0 ng/mL) more efficiently than oral administration of D_2 increased plasma D_2 (49.1 ± 32.6 ng/mL) and 25(OH) D_2 (27.9 ±2.1 ng/mL). The D_3 given after an oral dose of D_2 was less efficient for increasing plasma concentrations of 25(OH)D_3 (61.2 ± 12.0 ng/mL) compared with D_3 given without previous D_2 administration (103.5 ± 10.0 ng/mL), whereas the plasma concentrations of D_3 itself were the same when given first (182.6 ± 17.1 ng/ mL) as when given after D_2 (200.0 ± 123.9 ng/mL). The same occurred for plasma concentrations of D_2 metabolites both if D_2 was given first (49.1 ± 32.6 ng/ mL) and after D_3 (54.7 ± 7.7 ng/mL). In conclusion, D_3 given after D_2 is less efficient at increasing the plasma status of 25(OH)D_3 than D_3 given without previous D_2 administration.