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

摘要: 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 housed an environmental chamber at about 19°C, 50% relative humidity, 16 h of light 8 h darkness (lights on 0700 h); fed daily 0900 h; milked 0830 2000 h. Peripheral concentrations all exhibited weak rhythms—average minima 3.1 ng/ml 1800 h, maxima 4.5 ng/ml 0530 h—and strong rhythms with periods around 120 min. Peak to trough amplitudes rhythms, 1 17 ng/ml, varied among within time. No direct relation between peaks milking or feeding was apparent. Spectral analysis indicated that most power (variation) centered cycle every 2 h, i.e., a period This very strong, easily observable, rhythm indicates oscillation 120 min is probably intrinsic mechanisms regulating peripheral glucocorticoid concentrations.