Reduced locomotor play behaviour of dairy calves following separation from the mother reflects their response to reduced energy intake

• The locomotor play of nursed calves separated from their mothers reflects their energy intake after separation.
• Calves prior access to automated milk feeders increased play and reduced vocalizations after separation due to an increased energy intake.

Play behaviour is an indicator of good welfare in young calves and is reduced by low energy intake and weaning off milk. There is renewed interest in keeping calves longer with the cow but separation leads to signs of distress, such as vocalizations. Providing calves with an alternative milk source prior to separation helps them adapt to the separation. We hypothesized that (1) locomotor play of nursed calves separated from their mothers will reflect their energy intake after separation, and (2) calves’ prior access to automated milk feeders will increase locomotor play and reduce vocalizations after separation due to an increased energy intake. 30 Holstein cows and their calves were kept in adjacent pens. “Suckling-only” calves were allowed to suckle the cow during the night and received no other milk, “Milk-feeder only” calves could obtain 12 L/day milk only from an automated milk feeder while “Suckling-and-milk-feeder” calves could suckle during the night and were allowed 12 L/day of milk from an automated milk feeder. At 6 weeks of age, calves were not allowed to enter the cow pen during the night but had access to automated milk and grain feeders. To measure locomotor play, we placed the calves individually in a 9.5 m × 2 m arena for 10 min, 10 times before and after separation. The frequency of jumping and vocalization were scored. Digestible energy (DE) intakes of the calves after separation were calculated from combined milk and grain intake. Before separation, there were no differences between the treatment groups on any behavioural measure (P > 0.10). For Suckling-only calves, there was a marked decrease in the frequency of jumping (Wilcoxon test, P = 0.02) and a marked increase in the frequency of vocalization during the first 3 days after separation (P = 0.004). During the first 3 days of separation, Suckling-only calves had a lower frequency of jumping (Mann–Whitney test, P = 0.009) and vocalized more frequently (Mann–Whitney test, P = 0.009) than did calves of the other treatment groups. For all calves, the number of vocalization was negatively correlated with frequency of jumping (rs = −0.51; P = 0.005). After separation, Suckling-only calves had lower energy intakes than calves of the other treatment groups (Mann–Whitney test, P = 0.01) and the digestible energy intake of the calves was positively correlated with the frequency of jumping (rs = 0.75; P < 0.001), and negatively correlated with the frequency of vocalization (rs = −0.59; P < 0.001). There were no differences between treatment groups five or more days after separation. Our results show that a low energy intake of calves after separation from the mothers is associated with reduced locomotor play and increased vocalization and that prior access to an automated milk feeder helps maintain energy intake after separation, which results in increased locomotor play. The association between vocalization and locomotor play suggests that the reduction in play at separation may be related to the emotional response of the calves to the decrease in energy intake.