Transitory Changes of Hormones in Plasma of Postpartum Dairy Cows

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Abstract
Changes in concentrations of luteinizing hormone [LH] estradiol-17.beta. and progesterone in blood plasma of 10 dairy cows were measured hourly for 10 h by radioimmunoassay on days 2 or 3, 7 or 8, and 12 or 13 postpartum. Comparisons were between mean hormone concentrations and hormone activity on each collection day postpartum. Mean concentrations of LH in plasma increased from postpartum days 2 or 3 to 7 or 8 to 12 or 13 as did the daily maximum change and activity index. Higher activity indexes for LH on days 7 to 8 and 12 or 13 as compared with days 2 or 3 postpartum were due primarily to increases in the magnitude and frequency of changes among individual cows whereas the increase in activity on days 12 or 13 as compared with days 7 or 8 was due to increased frequency. The magnitude of fluctuations of LH was variable, and changes normally persisted for only 1 hourly collection. Concentrations in plasma and activity of estradiol-17.beta. for individual cows during the postpartum period did not differ among days. Changes in estradiol-17.beta. were variable and persisted for 1-6 consecutive hourly collections.