Effects of the rearing environment complexity on laying hens' spatial cognition: A holeboard test approach

The rearing environment of layer chicks can differ greatly in degree of complexity. With the industry moving towards cage-free housing systems, greater demands are placed on the birds’ cognitive abilities in order for them to find resources such as food, water and nest-boxes. Because early environmental complexity can influence cognition, we aimed at increasing our knowledge of how two different rearing environments affect the cognitive abilities of the hens. We habituated 64 hens to a spatial holeboard test, half of which were reared in cages and the other half in an aviary. Out of these 64 hens, 14 cage- and 14 aviary-reared White Leghorn hens were tested twice a day every workday in a holeboard test from 32 to 40 weeks of age. The test consisted of 4 consecutive phases, namely the uncued, cued, over-training and reversal phases, during which the hens had to find baits in a subset of cups in an arena. All cups were identical, so hens had to rely on spatial cues to find the baits which were always hidden in the same cups. During the cued phase, cues were added to the baited cups to give additional information to the hens. During the reversal phase, baits were hidden in a new subset of cups to study cognitive flexibility. The results show the birds were able to successfully complete the task. Aviary-reared hens had a higher reference memory score than cage-reared hens in the first block of the cued phase (F_1,26 = 4.21, p < 0.05). Cage-reared hens also had a significantly higher latency to find the first bait than the aviary-reared hens for the uncued, cued and over-training phases (F_1,26 = 5.26, p < 0.03; F_1,26 = 6.32, p < 0.02; F_1,26 = 6.29, p < 0.02). The same was observed for the transition between them (uncued-cued: F_1,26 = 6.19, p < 0.02; cued-over-training: F_1,26 = 5.87, p < 0.03). No significant treatment effects were found for the reversal phase. In conclusion, cage-reared hens were slower to find the first bait than aviary-reared hens and seemed to be more sensitive to changes in the environment, as shown by the differences during the transition between phases. Aviary-reared hens might therefore be better at adjusting to complex laying environments.