Vitamin D Metabolites in Plasma of Cows Fed a Prepartum Low-Calcium Diet for Prevention of Parturient Hypocalcemia

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Abstract
Changes in vitamin D metabolites of plasma were characterized in Jersey cows fed a prepartum low-Ca diet. Eight cows were fed a high-Ca diet (80 g/day) and 8 were fed a low-Ca diet (8 g/day) at least 14 days before parturition. Ca concentrations in plasma decreased after initiation of feeding either diet, but cows fed low-Ca diet tended to have lower prepartum Ca and P and greater peripartal Ca in plasma. Hydroxyproline in plasma was greater during peripartal period in cows fed low-Ca diet. Prepartum 1,25-dihydroxyvitamin D in plasma tended to be greater in cows fed low Ca. Increases in 1,25-dihydroxyvitamin D were 2 and 3 days after initiation of the low-Ca diet; during the first 2 days after parturition, 1,25-dihydroxyvitamin D tended to be lower in those cows fed low Ca. As parturition neared 24,25-dihydroxyvitamin D tended to be lower in cows fed the low-Ca diet. Usual early postpartum changes in Ca, P, Mg, 1,25-dihydroxyvitamin D and hydroxyproline were seen during first few days after initiation of feeding low Ca. The preventative action of the low-Ca diet apparently is associated with preparation of the Ca homeostatic mechanism several days before the Ca demand of initiation of lactation.