Relationships between Diurnal Variation in R-R Interval and Feeding Behavior in the Horse.

Abstract

Heart rate, R-R intervals and the number of jaw movements were measured simultaneously for a 24-h period in an adult horse in a housed free-moving state. Feeding behavior was characterized by the number of jaw movements. Dropped beats could be monitored from a series o f R-R intervals, and these dropped beats were regarded as second-degree A-V blocks. Thirty-eight dropped beats occurred during a 24-h period. Second-degree A-V blocks frequently occurred in the night (p<0.001) and scarcely occurred in the active feeding periods (p<0 .001). Moreover, the R-R interval periodically fluctuated at rest in the night. It was speculated that this periodical fluctuation in R-R interval is a respiratory sinus arrhythmia. This arrhythmia was not observed during feeding periods. A periodic violent fluctuation in the R-R intervals persisting for about 10 min was observed in the interval between feeding periods in the middle o f the night, and this episode might occur during paradoxical sleep (REM sleep).