Plasma Calcitonin-Like Activity and Urinary Cyclic Adenosine Monophosphate during Pregnancy, Parturition, and Lactation in Cows with Parturient Hypocalcemia

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Abstract
Plasma calcitonin-like (CT-like) activity was determined in 19 Jersey cows one month prepartum, at the time of parturition, 24 hours postpartum, and one month postpartum. At parturition 10 cows developed severe hypocalcemia (5.24 ± 0.26 mg/100ml) and demonstrated the pathognomonic clinical signs of parturient paresis. Plasma CT-like activity relative to either the serum concentration of calcium or phosphorus was significantly higher in the cows which developed parturient paresis compared to control parturient cows. A rise in plasma CT-like activity was observed in both groups of cows 24 hours postpartum even though serum calcium remained below prepartal levels. No significant difference in plasma CT-like activity could be demonstrated between control and diseased cows at one month prepartum and one month postpartum. The urinary excretion of cyclic adenosine monophosphate (c-AMP) was consistently lower at each interval in cows which developed parturient paresis compared to control cows. The results of this investigation suggest that the secretion of calcitonin by the parafollicular cells in cows which develop parturient hypocalcemia and paresis escapes from the precise control by blood calcium near parturition and secretion remains elevated despite the severe hypocalcemia.

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