The entrainment of caecotrophy-rhythm of the rabbit following 6- and 12-h phase-shifts of the Zeitgeber.

By means of automatic registration of hard faeces excretion the caecotrophy-rhythm of 10 rabbits was monitored. In the animals a negative phase angle difference existed between 'lights on' and the start of caecotrophy in LD 12:12. Five rabbits practised caecotrophy once and 5 rabbits twice/24 h. Following 6-h phase-shifts of the LD-regimen the caecotrophy-rhythm was shifted in the same direction as the Zeitgeber. The time of re-entrainment for advance shifts of caecotrophy is significantly longer than for delay shifts. The inversion of the Zeitgeber causes caecotrophy to be delay-shifted in all animals.