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Circadian and Ultradian Rhythms of Peripheral Cortisol Concentrations in Lactating Dairy Cows

1993; Elsevier BV; Volume: 76; Issue: 9 Linguagem: Inglês

10.3168/jds.s0022-0302(93)77595-5

1529-9066

Alan M. Lefcourt, Joel Bitman, S. Kahl, David Wood,

Animal Behavior and Welfare Studies

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 degrees 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.