We investigated the synchronization of behavioural responses of calves at weaning using time-lag weaning method. Six 4-month-old Japanese Black Cattle calves were used as experimental animals. They were divided into control (n=3) and delayed weaning groups (n=3). Then they weaned in pairs. During the eight-day experiment, DW calves were weaned a day after control calves. We observed vocalization and self-grooming of each calf through continuous observations. Maintenance behaviours (lying at rest, eating, and walking) and changes of location in the experimental paddock were recorded by 1-min instantaneous sampling. Vocalizations during the week following separation and self-grooming during the week and during each observation day were compared among pairs using the Mann-Whitney U-test. The paddock was divided into three blocks: front, centre, and back. The concordance rates of the staying blocks were calculated. Furthermore, the rate of movement (m/h) was measured for each pair and was used for comparison. Vocalizations of control calves were more numerous than those of the DW group (control, 3641±673 calls; DW, 3384±715 calls), but not significantly so. Furthermore, the groups' vocalization peaks differed. Self-grooming incidences were significantly more numerous in the control group than in the DW group: 291±56 times, 122±36 times, respectively. A significant difference was found during 3-6 days after weaning (P<0.05). Regarding maintenance behaviour, the transitions of eating and walking were similar in each pair. The concordance rates of the staying blocks were extremely high among experimental pairs: 95.6%, 86.6%, and 82.1%, respectively. A moving distance peak was observed in the second day the DW group (the second day of control). The transition was similar for each pair. These results suggest high synchronization of the maintenance behaviour and activity at weaning. However, vocalizations might have strong severalty.

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