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National Animal Disease Center, Agricultural Research Service, US Department of Agriculture, Ames, IA 50010
ABSTRACT
Intravenous infusion of synthetic bovine parathyroid hormone for 96 h increased 1,25-dihydroxyvitamin D, Mg, Ca, and hydroxyproline in plasma of pregnant cows within 16, 24, 48, and 72 h, respectively. Plasma Ca concentration was maximal at the end of the 96-h infusion (15.1 mg/100 ml). Plasma concentration of 1,25-dihydroxyvitamin D at 96 h was twice that before parathyroid hormone infusion, indicating that parathyroid hormone stimulated 1,25-dihydroxyvitamin D production in the presence of hypercalcemia. The urinary excretion of hydroxyproline indicated that at least 48 h of parathyroid hormone stimulation was required to stimulate bone resorption in the pregnant cow.
Eight periparturient cows were on a high Ca diet prepartum. Four cows were treated with intravenous parathyroid hormone prior to parturition. Four cows were untreated. All four untreated cows developed parturient paresis. None of the cows treated with parathyroid hormone developed parturient paresis. However, two cows that received parathyroid hormone for <24 h prior to parturition became hypocalcemic, but not recumbent. Plasma Ca concentrations remained within normal limits in the two other cows that received >60 h parathyroid hormone infusion prior to parturition. We conclude that exogenous parathyroid hormone (1–34) can prevent parturient paresis if administered at least 60 h prior to parturition.
1 This research supported in part by Binational Agricultural Research and Development Grant #US-352-81.
2 US Department of Agriculture, National Program Staff, Building 005, Room 206, Beltsville Agricultural Research Center-West, Beltsville, MD 20705.
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