The effect of group composition and age on social behavior and competition in groups of weaned dairy calves

The objective of the present study was to investigate how group composition affects behavior and weight gain of newly weaned dairy calves and how age within heterogeneous groups affects behavior and competition. Seventy-two calves were introduced into 6 groups of 12 calves, of which 3 groups were homogeneous and 3 groups were heterogeneous (including 6 young and 6 old calves). The 9.8 m × 9.5 m large experimental pen had 4 separate lying areas as well as a feeding area. Behavior and subgrouping were recorded on d 1, 7, and 14 after grouping, and calves were weighed before and after the experimental period of 14 d. Analysis of the effect of group composition on behavior and weight gain included young calves in heterogeneous groups and calves in homogeneous groups within the same age range at grouping (30 to 42 d). Irrespective of group composition, time spent feeding and lying increased, whereas time spent active decreased from d 1 to 7. In homogeneous groups, calves were more explorative on d 1 after grouping. Finally, calves in homogeneous groups had a higher average daily weight gain than calves in heterogeneous groups. Analysis of the effect of age included young and old calves of heterogeneous groups. Young calves were less explorative than old calves. Young calves were more active than old calves on d 1 but less active on d 7. Time spent lying and lying alone increased over time. More displacements from the feed manger were performed by old calves than by young calves. An analysis including all calves in both homogeneous and heterogeneous groups showed that when lying, calves were evenly distributed on the 4 lying areas and formed subgroups of on average 3 calves. In conclusion, age heterogeneity leads to increased competition, which may have a negative influence on the young calves' performance.