Exposing avian embryos to light affects post-hatch anti-predator fear responses
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2016 Elsevier B.V. Environmental stimuli present during incubation can impact the behavior of birds post-hatch. To determine the effect of exposing broiler chicken embryos to light on fear-related behavior post-hatch, we conducted two experiments in which we incubated eggs under various light schedules, and then measured fear responses when the chickens (N=720) were 36 wk of age. In Expt. 1, the incubation photoperiods were 0L:24D, 12L:12D, and 24L:0D, and tonic immobility (TI) and inversion (INV) tests were administered. In Expt. 2, the incubation photoperiods were 0L:24D, 1L:23D, 6L:18D, and 12L:12D; and an approach test (APPR) and an emergence (EMRG) test were administered in addition to TI and INV. In Expt. 1, both 12L:12D and 24L:0D had shorter latencies to right during TI (213.523.7 and 231.824.2s, respectively) than 0L:24D (305.526.1s) and also wing flapped less intensely during INV (12L:12D 5.00.1 wing flaps; 24L:0D 5.40.2) than 0L:24D (5.70.1). In Expt. 2, the 12L:12D birds once again had shorter latencies to right during TI (120.016.5s) and wing flapped less intensely during INV (4.70.1 wing flaps) than 0L:24D (201.424.9 and 5.50.1, respectively). They also had shorter latencies to exit the dark box in EMRG (28.93.3s), and were less active (282%), vocalized less (178.89.3 times/3min) and spent more time closer to the observer during APPR (633%) than 0L:12D (42.95.0s, 353%, 211.210.4 times/3min, 513). The 1L:23D and 6L:18D showed some reductions in fearfulness compared to 0L:24D, but these were not consistent across tests. The 6L:18D and 12L:12D birds demonstrated lateralization in the direction to leave the box in EMRG, whereas 1L:23D and 0L:12D exited left or right at chance levels. The results of these experiments indicate that providing at 12h of light stimulation daily during embryogenesis results in long-term reductions in fearfulness as measured by multiple tests, and that this may be related to cerebral lateralization. In conjunction with other research, these findings show that light exposure during embryogenesis has important implications for behavioral phenotypes and welfare in chickens.
