Effect of Parathyroid Hormone on Calcium and Other Plasma Constituents of Dairy Cattle near Parturition

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Abstract
The administration of parathyroid extract within 2 hr postpartum to 1st calf heifers, normal mature cows, and mature cows with a past history of milk fever did not appreciably alter their plasma levels of calcium, magnesium, or alkaline phosphatase. Plasma inorganic phosphorus was increased moderately in most of the animals by the action of parathyroid extract Mature cows showed a greater decrease in calcium and inorganic phosphorus and a greater increase in magnesium at parturition than did first-calf heifers. Alkaline phosphatase remained relatively constant in all animals. Data from 31 parturitions and 6 cases of milk fever suggest that milk fever can result from either a low level of Ca or a low level of both P and Ca. Cases of milk fever which relapsed were of the latter type. Parturient cows were not responsive to parathyroid extract and its administration just after calving had no apparent effect on the occurrence or severity of milk fever.