Social housing improves dairy calves' performance in a competition test.

On most dairy farms, calves are housed individually until weaning. However, depriving calves of an early social environment impairs behavioral development. We studied the effect of early-life social housing on calves' competitive skills. In this study, Holstein heifers were pseudorandomly assigned to either individual housing (n = 9) or pair housing (with a nonfocal companion, n = 9) at the age of 11 d. After 14 d of housing treatment, calves underwent a competition test for milk access against a group-reared calf; consisting of 2 test sessions per day for 5 d (session duration: 74.42 ± 2.29 s; mean ± standard error). Pair-housed calves performed better than individually housed calves: throughout the competition days, individually housed calves increased their latency to approach the milk bottle and decreased their time spent drinking in contrast to pair-housed calves, which exhibited stable latencies to reach the milk bottle and increased their time drinking. To control for the influence of personality on their competitive abilities, all calves were subjected to personality tests assessing boldness before being exposed to the housing treatment. Our findings indicate that calves assessed as bolder during the pretreatment personality test tended to approach the milk bottle faster. Our results provide additional evidence of the beneficial effects of social housing on dairy calves' behavioral development.