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Effect of vertical complexity of rearing environment on the ontogeny of depth perception in laying hens

Abstract

Multi-tiered aviary systems provide laying hens with opportunities for species-specific behaviors, including vertical and horizontal movement. However, collisions and failed landings that occur during vertical movement can be associated with injuries, such as keel bone fractures. Previous studies have suggested that floor rearing of pullets with minimal access to elevated structures may negatively impact adult laying hens’ ability to navigate vertical space. Unfortunately, it is not clear whether this is due to deficits in physical ability or if differences in rearing environment influence the development of adequate spatial cognition. The effect of rearing environment on the development of spatial cognition was investigated in egg-laying hens using a novel Y-maze task and a visual cliff task at 7-8, 15-16, and 29-30 weeks of age. Dekalb White pullets (n = 450) were reared in three different environments until 16 weeks of age: floor, single-tier aviary, and multi-tier aviary. At 16 weeks, all birds received a multi-tier aviary for the laying period. Distance perception was evaluated via a Y-maze task with a ratio of 1:3 or 1:1 difference in escape arm length and exit choice was recorded. To evaluate depth perception, hens were placed on a perch in the center of the visual cliff table, facing the perceptual cliff. Each bird was tested with three trials with random assignment of cliff depth at 15, 30, and 90 cm below the perch. Birds were given the option of escaping by jumping to a platform suspended over the visual cliff. Behaviors recorded included crossing the visual cliff and number of downward head orientations over the cliff edge. It was found that birds, regardless of age and rearing treatment, exited the Y-maze through the shorter (0.70, P < .001) arm more than chance. An interaction effect of age and rearing treatment on crossing the visual cliff (Wald x2 = 12.734, df = 4, p = 0.013) was found, with hens reared on the floor being less likely to cross the visual cliff at 8 and 16 weeks of age than 30 week old floor reared birds or multi and single treatment birds at 8 and 30 weeks old. These results suggest that floor reared birds do not have impaired depth perception, but do respond differently when faced with a vertical structure prior to being transitioned to adult housing. This has implications for pullet rearing and the importance of early access to vertical structures.

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