Bar, A., Agricultural Research Organization, Institute of Animal Science, Volcani Center, Bet Dagan, Israel
Perlman, R., Agricultural Research Organization, Institute of Animal Science, Volcani Center, Bet Dagan, Israel
Sachs, M., Agricultural Research Organization, Institute of Animal Science, Volcani Center, Bet Dagan, Israel

Israeli Friesian cows in the third or later lactation, were injected intramuscularly with 1α-hydroxyvitamin D3 in propylene glycol. Plasma 1α-hydroxyvitamm D3 peaked 24 to 48 h after 700 μg of the drug was injected and decreased to the initial concentration 4 d later. The disappearance rate of 1α-hydroxyvitamin D3 from the blood was .330 d−1 (biological half-life of 2.1 d). Plasma 1,25-dihydroxyvitamin D3 peaked 24 to 48 h after the injection and approached the initial concentration 5 to 7 d later. Plasma calcium increased within 24 h, reached a plateau at 4 to 6 d, and then decreased. Administration of 700 μg 1α-hydroxyvitamin D3 resulted in higher plasma 1,25-dihydroxyvitamin D3 and calcium concentrations than when 350 μg of the drug was injected, 1α-Hydroxyvitamin D3 did not affect plasma hydroxyproline. The injection of 700 μg 1α-hydroxyvitamin D3 52 to 36 h before parturition resulted in a greater increase in plasma 1,25-dihydroxyvitamin D3 than that obtained with 350 μg. In both groups 1,25-dihydroxyvitamin D3 peaked 24 h after injection, as opposed to the controls, which peaked 72 h postpartum. At parturition, the 700-μg dose resulted in a slight hypercalcemia; the 350-μg dose moderated the hypocalcemia prevalent during this period, whereas in controls hypocalcemia was more pronounced. In cows injected with 700 μg, hypercalcemia was observed until the 15th d postpartum. Plasma hydroxyproline was elevated in all cows 48 to 72 h after parturition, but the increase was smaller in animals injected with 1α-hydroxyvitamin D3. Results suggest that for prevention of bovine parturient paresis a single injection of 700 μg 1α-hydroxyvitamin D3 may be more effective than 350 μg. The potential danger of delayed milk fever, as a result of extended hypercalcemia, has still to be evaluated. © 1985, American Dairy Science Association. All rights reserved.