The Study on Vitamin D₃ Metabolism in Dairy Cows with Special Referenee to Serum Levels of Vitamin D₃ Metabolites

Abstract

To study the metabolism of vitamin D₃ in dairy cows, the serum levels of vitamin D₃ metabolites were determined in healthy dairy cows raised on normal ration. Newborn, young and adult cows and vitamin D₃ administrated adult cows were used in the experiment. Serum levels of 1α, 25-dihydroxyvitamin D₃ and 24(R), 25-dihydroxyvitamin D₃ in the newborn calves were higher compared with those in young and adult cows, whereas serum 25-hydroxyvitamin D₃ levels was not changed in those three groups. On the other hand, daily administration of 10, 000 IU vitamin D₃ to adult cows resulted in the increases of serum 25-hydroxyvitamin D₃ and 24(R), 25-dihydroxyvitamin D₃ levels. However, serum 1α, 25-dihydroxyvitamin D₃ levels in those cows were not different from those in adult cows which did not receive vitamin D₃. Whereas single administration of 150, 000 IU vitamin D₃ showed a slight increase in serum 25-hydroxyvitamin D₃ and 24(R), 25-dihydroxyvitamin D₃, and a significant increase in serum 1α, 25-dihydroxyvitamin D₃. Correlation between serum vitamin D₃ metabolites and serum Ca, P or Mg concentration was not observed. However, correlation was observed between 24(R), 25-dihydroxyvitamin D₃ and 25-hydroxyvitamin D₃. Serum 1α, 25-dihydroxyvitamin D₃ was maintained relatively constant level, except for newborn calves and adult cows treated with 150, 000 IU vitamin D₃. However, serum levels of 25-hydroxyvitamin D₃ and 24(R), 25-dihydroxyvitamin D₃ vatied in a certain degree directly proportional to intake of vitamin D₃.