Is the metabolism of 25-hydroxyvitamin D3 age-dependent in dairy cows?

It has recently been demonstrated that prepartum administered 25-hydroxyvitamin D-3 (25-OHD3) is a promising candidate to assist the maintenance of peripartal calcium homeostasis in dairy cows. Since the incidence of peripartal hypocalcemia and the reported beneficial effects of the treatment are both associated with the lactation number, we investigated pharmacokinetic aspects of 25-OHD3 related to the age of dairy cows. The daily oral administration of 3 mg 25-OHD3 in rapeseed oil as well as a treatment with 4 and 6 mg included in the feed during the last eight to ten days of gestation resulted in linear dosage- and age-dependent increases in plasma 25-OHD3. After parturition the administration was stopped and blood samples were taken to calculate the plasma half-life. Irrespective of the supplemented dosage, cows starting the 2nd lactation showed a significantly longer plasma half-life of 25-OHD3 than cows starting the 3rd or higher lactation. Age-dependent differences in the increase of plasma 25-OHD3 could already be found before parturition when calcium homeostasis was not yet significantly challenged. Additionally, no correlations between plasma half-life of 25-OHD3 and 1,25-dihydroxyvitamin D-3, PTH or the bone resorption marker CrossLaps were observed after parturition. Thus we conclude that the influence of the lactation number on the pharmacokinetics of 25-OHD3 is related directly to the age of the cows. This article is part of a Special Issue entitled 'Vitamin D Workshop'. (c) 2012 Elsevier Ltd, All rights reserved.