Does dairy calves' motivation for social play behaviour build up over time?

Dairy calves are often housed in individual pens, which limits play behaviour. This study investigates whether the motivation for social play builds up during periods of deprivation hereof. Sixteen mixed-sex pairs of calves (33 +/- 3 days of age) were housed in pair pens for 1 week and then separated into adjacent single pens. In each of two successive weeks, in a cross-over design, the pairs of calves were given access to an arena (3.6 m x 7.10 m) for 45 min on two consecutive days followed by deprivation of arena access for 4 days or 0 days before being tested on the seventh day. On test days, health was scored for all calves. The bull calf of each pair was chosen as focal calf. The behaviour of the focal calf was recorded during the 20-min test. When deprived of arena access for 4 days, calves performed more parallel locomotor play than when deprived for 0 days (P < 0.001). Calves performed more frontal pushing in the second week of the study (P < 0.001). Calves performed less frontal pushing (social play) (P < 0.05) and tended to perform more individual locomotor play (P = 0.05) with increasing (worse) companion calf health score. The results suggest that the motivation for some, but not all, elements of calf play behaviour builds up over time. Thus, differentiating between elements of play may be important in the use of calf play behaviour to assess animal welfare. The association between the health of the companion calf and frontal pushing suggests that a healthier calf stimulates more social play.