Early life environment and adult enrichment: effects on fearfulness in laying hens

The environmental complexity, both during early and adult life, contributes to shaping individuals’ fearfulness. The present study aimed at testing whether hens reared in an aviary were less fearful than hens reared in cages, and whether provision of additional enrichment during the laying phase could reduce fearfulness. We used White Leghorn laying hens (N = 384) reared in cages (N = 192) or in an aviary (N = 192) and then housed in furnished cages from 18 weeks of age, with or without the provision of additional enrichment. We tested naïve hens at 31 and 60 weeks of age in a novel object test and at 33 and 61 weeks of age in an open field test. Cage-reared hens had a latency to approach the novel object comparable to the one of aviary-reared hens when tested at 31 weeks of age (F₁, ₁₇ = 2.71; p = 0.12). At 60 weeks of age, birds housed in additionally enriched furnished cages were significantly faster to approach a novel object than birds housed in standard furnished cages for both rearing conditions (F₁, ₆₁ = 19.02; p < 0.01). Hens reared in cages walked distances comparable to aviary-reared hens in the open field arena at 33 and 61 weeks of age (t = -0.33; p = 0.75 and X² (1, N=123) = 0.02; p = 0.89, respectively), and the provision of additional enrichment during the laying phase did not increase that distance (X² (1, N = 1²3) = 2.01; p = 0.16). We also did not observe any differences in the latency to start moving in the arena (p > 0.05). These results suggest that the environmental complexity during rearing had no medium- and long-term effects on fearfulness measured in the open field and novel object test. However, additional environmental enrichment during the laying phase had a stronger influence, reducing fearfulness towards novelty. This study suggests that environmental enrichment during adulthood can have positive effects on laying hens’ fearfulness.