title: Circadian and ultradian rhythms of peripheral cortisol concentrations in lactating dairy cows.
abstract: 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.
authors.affiliation: USDA Livestock and Poultry Sciences Institute, Beltsville, MD 20705.
authors.forename: A M
authors.initials: AM
authors.lastname: Lefcourt
authors.forename: J
authors.initials: J
authors.lastname: Bitman
authors.forename: S
authors.initials: S
authors.lastname: Kahl
authors.forename: D L
authors.initials: DL
authors.lastname: Wood
mesh_terms: D000204:Activity Cycles; D000818:Animals; D002417:Cattle / Q000502:physiology*; D002940:Circadian Rhythm; D005260:Female; D006854:Hydrocortisone / Q000097:blood*; D007774:Lactation / Q000502:physiology*
chemical_list: D006854:Hydrocortisone