Evidence that discrimination against ergocalciferol by the chick is the result of enhanced metabolic clearance rates for its mono- and dihydroxylated metabolites

J Nutr. 1988 May;118(5):633-8. doi: 10.1093/jn/118.5.633.


Studies on the discrimination between ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3) by chickens have led to conflicting conclusions. To investigate this problem in more detail, radiolabeled vitamin D and vitamin D metabolites were administered intravenously, which allowed determination of their relative plasma clearance rates. The study involved three groups of adult male chickens (five per group). Birds in group 1 were co-dosed with [3H]vitamin D2 and [3H]vitamin D3. Birds in group 2 were co-dosed with [3H]25-dihydroxyvitamin D2 and [3H]25-dihydroxyvitamin D3 and birds in group 3 were co-dosed with [3H]1,25-dihydroxyvitamin D3 and [3H]1,25-dihydroxyvitamin D2. The results indicated that the plasma turnover rate of [3H]vitamin D2 is 1.5 times faster than that of [3H]vitamin D3. Plasma turnover of the 25-hydroxylated metabolites differed, with [3H]25-dihydroxyvitamin D2 clearing faster (11 times) than [3H]25-dihydroxyvitamin D3. The largest difference appeared in the 1,25-dihydroxyvitamin D2 turnover rates with 1,25-dihydroxyvitamin D2 clearing approximately 33 times faster then [3H]1,25-dihydroxyvitamin D3. These data, therefore, indicate that discrimination against vitamin D2 sterols in the chick occurs primarily between steps in the metabolism of vitamin D and not at the point of metabolism or excretion of the parent vitamin.

MeSH terms

  • 25-Hydroxyvitamin D 2
  • Animals
  • Calcifediol / pharmacokinetics
  • Calcitriol / pharmacokinetics
  • Chickens / metabolism*
  • Cholecalciferol / pharmacokinetics*
  • Ergocalciferols / analogs & derivatives
  • Ergocalciferols / pharmacokinetics*
  • Male
  • Metabolic Clearance Rate


  • Ergocalciferols
  • Cholecalciferol
  • 25-Hydroxyvitamin D 2
  • 1,25-dihydroxyergocalciferol
  • Calcitriol
  • Calcifediol