Effects of the early social environment on behavioral responses of dairy calves to novel events.

Providing young animals the opportunity to engage in more complex social interactions is hypothesized to improve their capacity to cope with changing environments. To test the effects of the early social environment on the behavioral responses of dairy calves to novelty we compared (1) individual with pair housing and (2) group housing with companions of similar age with group housing with a more experienced conspecific. Fifty-four dairy calves were separated from the cow soon after birth and housed individually (n=6 calves) or in pairs (n=6 pairs), or in pens composed of groups of 3 young calves (n=6 groups) or groups of 2 young calves and an older calf (n=6 groups). At 65 to 69 d of age, calf responses were tested in an environmental novelty test and a social novelty test. Individually housed calves were more active [i.e., spent less time standing (means ± SEM): 201.4 vs. 280.3±30.5 s/test; and more time running: 83.2 vs. 57.3±19.1 s/test] and more reactive (i.e., defecated more frequently; 1.3 vs. 0.6±0.2 events/test) when tested in the novel arena, compared with pair-housed calves. During the social novelty test, individually housed calves spent less time running (51.8 vs. 96.4±11.6 s/test), showed a longer latency to socially interact (111.1 vs. 20.4±21.7 s/test), and spent more time involved in social interactions (130.7 vs. 79.7±19.0 s/test) with the unfamiliar calf than did pair-housed calves. Individually housed calves were also more reactive to the presence of an unfamiliar calf as indicated by increased rates of defecation (2.3 vs. 0.7±0.5 events/test) and kicking (2.2 vs. 0.7±0.4 events/test) compared with pair-housed calves. Calves housed in groups with an older companion were more reactive to the novel environment than were calves housed in groups of similar age: they defecated (1.0 vs. 0.6±0.2 events/test) and vocalized (23.6 vs. 15.3±3.8 events/test) more during the test. These calves also spent less time exploring (266.3 vs. 355.0±27.4 events/test) and had a lower frequency of kicking (0.1 vs. 2.0±0.5 events/test) when tested with an unfamiliar calf. We conclude that calves housed individually are more reactive to environmental and social novelty when compared with calves housed in pairs and that calves housed with an older companion are less reactive to a novel calf when compared with calves housed in groups of similar age.