Pharmacokinetics and amounts of 25-hydroxycholecalciferol in sheep affected by osteodystrophy.

Amounts of 25-hydroxycholecalciferol in plasma were measured in two groups (A and B) of lambs (Experiment 1) and in two groups (C and D) of wethers (Experiment 2). Groups A (eight lambs) and C (nine wethers) consisted of animals born and raised in total confinement; these animals exhibited an osteodystrophic condition. Groups B (four lambs) and D (10 wethers) consisted of healthy animals born and raised in a conventional barn with free access to an open barn yard (i.e. exposure to sunshine). The 25-hydroxycholecalciferol in plasma of both groups of sick animals, Group A (12.9 ng/ml) and Group C (18.0 ng/ml), were lower than the amounts of the two corresponding groups of healthy animals. Group B (29.2 ng/ml and Group D (32.5 ng/ml). Pharmacokinetic analysis of 25-hydroxycholecalciferol in affected lambs following intramuscular injection of 1,000,000 IU vitamin D3 indicated that transport of vitamin D3 from the site of injection to the liver and its metabolism to 25-hydroxycholecalciferol were rapid. Peak 25-hydroxycholecalciferol occurred at .6 wk, and half-life was 3.1 wk.