Dose response to vaginal administration of 1,25-dihydroxyvitamin D3 to cows

It was previously reported that intravaginal (IVAG) administration of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) might be protective against bovine hypocalcaemia. In the present study, various doses of exogenous 1,25(OH)2D3 were administered IVAG to ovariectomised cows, and the subsequent changes in the biochemical parameters of the blood were measured to assess the characteristics of vaginal absorption. Five cows received 1,25(OH)2D3 IVAG at a dose of 0.125, 0.25, 0.5, or 1.0 μg/kg of body weight (BW) or intravenously at a dose of 1.0 μg/kg BW. Dosing was at intervals of at least two weeks in a 5 × 5 Latin square design. Vaginally administered 1,25(OH)2D3 was absorbed in a dose-dependent manner. There was no correlation between the IVAG dose of 1,25(OH)2D3 and subsequent changes in plasma calcium concentrations. The bioavailability of 1,25(OH)2D3 administered IVAG at 1.0 μg/kg BW was approximately 93%.