Endogenous oscillator and regulatory mechanisms of body temperature in sheep.

To determine the influence of various feeding schedules (different times of feeding, times without feeding) on the time course of heart rate (HR), electric activity of cervical muscles (EMG), motor activity (ACT) and body temperature (TB) in ruminants, 5 sheep were equipped with portable dataloggers able to register and store these variables every 30s. Under controlled housing conditions, the temporal changes which occur were registered for 12 consecutive days each period at least. During experimental periods with various feeding times HR and TB were within the physiological range and all variables showed pronounced peaks which were associated with the time of food presentation. On days without feeding TB (38.8 degrees C) was at the lower limit of this range and HR (56 bpm) was extremely below this limit; similar peaks as before were not detectable. The circadian rhythms of HR and TB seemed not to be influenced by the different times of feeding, but there were hints, that photic or social factors could act as a zeitgeber for ACT. Remarkable was the fact that the downregulation of the food induced rises of HR and TB was determined by the phase angle of the circadian rhythm.