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Journal of Dairy Science Vol. 76 No. 9 2607-2612
© 1993 by American Dairy Science Association ®
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Circadian and Ultradian Rhythms of Peripheral Cortisol Concentrations in Lactating Dairy Cows

A. M. Lefcourt 1, J. Bitman 1, S. Kahl 1, and D. L. Wood 1

1 Agricultural Research Service, USDA, Livestock and Poultry Sciences Institute, Beltsville, MD 20705

To investigate possible circadian and ultradian periodicities for plasma cortisol in lactating dairy cows, integrated 15-min blood samples taken sequentially over 48 h from six cows were analyzed by radioimmunoassay. The cows were housed in an environmental chamber at about 19°C. 50% relative humidity, and 16 h of light and 8 h of darkness (lights on at 0700 h); fed daily at 0900 h; and milked at 0830 and 2000 h. Peripheral concentrations of cortisol for all six cows exhibited weak circadian rhythms—average minima were 3.1 ng/ml at 1800 h, maxima were 4.5 ng/ml at 0530 h—and strong ultradian rhythms with periods around 120 min. Peak to trough amplitudes of ultradian rhythms, 1 to 17 ng/ml, varied among and within cows over time. No direct relation between ultradian peaks and milking or feeding was apparent. Spectral analysis indicated that most power (variation) was centered around 1 cycle every 2 h, i.e., around a period of 120 min. This very strong, easily observable, ultradian rhythm indicates that an oscillation with a period around 120 min is probably intrinsic to mechanisms regulating peripheral glucocorticoid concentrations.

Key Words: glucocorticoid • spectral analysis • ultradian rhythm • bovine

Submitted on January 15, 1993
Accepted on March 25, 1993




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