Fear and coping styles of outdoor-preferring, moderate-outdoor and indoor-preferring free-range laying hens

Abstract

Free-range systems are increasing in popularity as outdoor access is perceived to improve hen welfare, but radio-frequency identification tracking of individuals shows not all hens access the range daily with some hens never going outside. The individual variation in range use may be correlated with individual differences in fear and coping styles. In this study, tests of tonic immobility, manual restraint (coupled with plasma corticosterone responses) and open field were applied to ISA Brown hens ('Gallus gallus domesticus': n = 104) at 37-39 weeks of age. Focal hens were selected as categorised into three different range access groups based on the percentage of available days across the trial period that they went outdoors: indoor-preferring (accessed the range on 0-10% of available days), moderate-outdoor (accessed the range on 30-60% of available days), and outdoor-preferring (accessed the range on 100% of available days). The indoor-preferring hens produced fewer vocalisations during manual restraint compared to the moderate-outdoor and outdoor-preferring hens (P = 0.004) and tended to be slower to vocalise (P = 0.08) but no differences were found in latency to first struggle (P = 0.55), number of struggles (P = 0.44) or plasma corticosterone responses (P = 0.82). During the open field tests, the indoor-preferring and moderate-outdoor hens showed longer latencies to move and fewer squares were crossed compared to outdoor-preferring hens (P ≤ 0.009) but no differences were found in latency to first vocalise (P = 0.72) and total number of vocalisations (P = 0.91). There were no differences between range access groups in duration of tonic immobility (P = 0.14). These results show indoor-preferring hens have elevated fear levels, and a possible behavioural indication of a different coping style compared to outdoor-preferring hens, but the inconsistent results within the moderate-outdoor range access group warrant further investigation.