Abstract
To investigate the characteristics of the heart rate fluctuations of sheep in a summer heat environment, experiments were performed on eight adult male and female Japanese Corriedale sheep in August (summer heat conditions) and in November (autumn control conditions). High respiration rates (ca. 200/min) and significant increases in the rectal, skin, and fleece temperatures observed at summer experiments indicated heat-stressed conditions of the animals. Mean R-R intervals were significantly lengthened in summer although the standard deviation and the coefficient of variation of R-R intervals were not significantly changed. In the results of spectral analysis of heart rate fluctuations by FFT, powers of the very low frequency (under 0.04 Hz, VLF) and the low frequency (0.04 to under 0.15 Hz, LF) bands were significantly inceased in summer. The power of VLF band expressed as the percentage to the total power was significantly increased in summer, but in contrast, that of the high frequency (0.15 to under 1.07 Hz) band was significantly decreased. It is presumed from the results that the amplitudes of the cyclic fluctuations in heart rate at the very low frequency and the low frequency bands are increased in a summer heat environment in relation to the adaptive thermoregulatory changes in the respirocirculatory functions.
