Rearing complexity affects fearfulness and use of vertical space in adult laying hens

e complexity of the rearing environment is important for behavioral development in layinghens. is study aimed to test the hypothesis that laying hens reared in a complex aviarysystem would be less fearful and less sensitive to stress as adults than hens reared in barrencage environments. Laying hens (n=160) were reared in the same house, either kept insidethe aviary rows to imitate cages (n=80) or in the conventional aviary system (n=80). ebirds were then transported to the experimental facilities at 16 weeks of age and mix-housedin custom built pens. Two birds per treatment per pen where tested in human approach andnovel objct tests at 19 and 23 weeks of age. e results were analyzed by ANOVA on scores for afearfulness-related principal component, generated using principal component analysis. Flightresponses and the relationship between €ight response and fearfulness score were analyzed bylogistic regression. Use of vertical space was analyzed by Wilcoxon matched pairs signed ranktest. Aviary-reared (AV) birds had lower levels of fearfulness compared with cage-reared (C)birds both at 19 weeks (mean±std AV: 0.24±1.56; C: 0.74±1.72; F(1,19)=5.66; P=0.03) and at23 weeks (AV: -0.69±1.62; C: 0.19±2.11; F(1,19)=4.49; P=0.05) of age. At 19 weeks of age, moreaviary-reared birds tended to show a €ight response compared to cage-reared birds (OR=2.4;P=0.09) when initially exposed to a novel object. Rearing complexity did not a‚ect the €ightresponse at 23 weeks of age (OR=1.4; P=0.6). e odds ratio of showing a €ight response whenexposed to the novel object was not in€uenced by the principal component fearfulness score(OR=0.89; P=0.2). At 19 weeks of age, more aviary-reared birds spent time on the low perch(median, 25th-75th percentile AV: 20.8, 14.4-23.0; C: 12.5, 10.4-18.4; P=0.01), the elevatedplatform (AV: 19.2, 13.0-25; C: 12.1, 6.3-22.1; P=0.01) and upper perch (AV: 16.7, 10.4-23.0; C:5.2, 2.1-14.1; P<0.0001) compared to the cage-reared birds. However, at 23 weeks of age, thesedi‚erences were not detected (P>0.0001). Conclusively, increased environmental complexityduring rearing reduced fearfulness at 19 and 23 weeks of age and increased vertical space useat 19 weeks of age in laying hens.