The circadian rhythm of rumination

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Abstract
SUMMARY: Three experiments were carried out with adult sheep in order to estimate the effect of light and darkness in determining the incidence pattern of rumination.In the first experiment the jaw movements of four sheep were recorded when they were housed in cages in a single room. Continuous records were made before and after black-out was applied to the room in order to investigate the effects of times of lighting and of feeding. The results showed that under these conditions the pattern of ruminating behaviour changed with the lighting system used and that the different feeding times had no effect upon rumination.The first experiment was repeated with four sheep. Equal 12 h light or dark periods running from 10.00 and 22.00 h were applied and also days of continuous light or darkness. Food was given as equal meals at the beginning of each 12 h period. The results confirmed those of the first experiment and showed that rumination was greatest during the second half of each 12 h period of darkness. With permanent light or darkness rumination was least in the period from 10.00 to 16.00 h.An attempt was made in the third experiment to impose a 16 h cycle on four sheep. The results showed no adaptation to a 16 h ‘day’. Instead, behaviour was circadian and probably based on cues external to the experimental room.