Exposing avian embryos to light affects post-hatch anti-predator fear responses

Abstract

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 fearrelated 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 3-6 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 (213.5 ± 23.7 and 231.8 ± 24.2 sec, respectively) than 0L:24D (305.5 ±26.1 sec) and also wing flapped less intensely during INV (12L:12D 5.0 ±0.1 wing flaps; 24L:0D 5.4 ±0.2) than 0L:24D (5.7 ±0.1). In Expt. 2, the 12L:12D birds once again had shorter latencies to right during TI (120.0 ±16.5 sec) and wing flapped less intensely during INV (4.7 ± 0.1 wing flaps) than 0L:24D (201.2 ± 24.9 and 5.5 ± 0.1, respectively). They also had shorter latencies to exit the dark box in EMRG (28.9 ±3.3 seconds), and were less active (28 ± 2%), vocalized less (178.8 ± 9.3 times/3min) and spent more time closer to the observer during APPR (63 ± 3%) than 0L:12D(42.9 ± 5.0 seconds, 35 ± 3%, 211.2 ± 10.4 times/3 min, 51 ± 3). 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 12 hours of light stimulation daily g 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.

A Matter of Degree: Strength of Brain Asymmetry and Behaviour

“…This result was confirmed by Dharmaretnam and Rogers [77], who additionally found that the dark-incubated chicks made more distress calls during the dual task than did the light-exposed chicks. This was also confirmed more recently by Archer and Mench [78], who found that the effect extends to at least six weeks post-hatching. Since monitoring for predators while searching for food is a common demand in the natural environment, the results of these experiments demonstrate a survival-relevant function of having a lateralized brain.…”

Does Functional Lateralization in Birds Have any Implications for Their Welfare?

“…Compared to the dark-incubated chicks, all of the light-exposed chicks were less fearful on all of the measures, and the least fearful chicks were those exposed to light throughout incubation. In a subsequent study, Archer and Mench [91] confirmed the role of light exposure in reducing fear responses and recommended 12 hours of light exposure daily throughout incubation to reduce fear and improve welfare of chicks. Even as little as 6 hours of light per day was sufficient to reduce fear on some tests.…”

“…Whether or not this effect of light on post-hatching behaviour relates directly to the effect of light exposure on the development of lateralization has yet to be determined. However, differences in lateralization are likely to be involved, and Archer and Mench [91] did show effects of the light exposure on lateralization in tests of turning bias.…”

“…Further evidence that exposure of chicken eggs to light affects fear and stress responses after hatching has been provided by Archer and Mench [90,91]. Their study of 2014 reported that the hen leaves the nest, thereby exposing the eggs to light, more frequently during the last week of incubation than prior to that time, and she leaves the nest most often on day 19, a key time for light exposure to lead to visual lateralization.…”

Embryonic thermal manipulation has short and long-term effects on the development and the physiology of the Japanese quail

“…As birds are oviparous, the incubation conditions can be modified in order to study the impact of environmental challenges or stressors during embryogenesis, thus reducing the impact of the maternal influence. Incubation parameters such as temperature [2], light [3] or noise [4] are known to impact development and behavior. In a context of climate change, with an increase of global average temperature and the occurrence of extreme heatwaves [5], numerous studies have reported the utilization of the thermal-manipulation (TM) of eggs during the incubation period to improve the later-life heat tolerance of chickens [2,[6][7][8][9][10][11][12][13][14][15][16] and turkeys [17,18] or to modify muscle development in ducks [19][20][21].…”