Assessing the motivation of laying hens to outdoor space access

Abstract

The present study aimed at evaluating the motivation of laying hens to access outdoor space and their behavior under indoor and outdoor conditions. A total of 54 laying hens (White Leghorns) at 38 weeks of age were housed in two experimental groups: indoors, 3 replicates of 9 hens each (10 hens/m²), and outdoors, 3 replicates of 9 hens each (10 m²/hen). The behavioral evaluation was performed using a video recording system, and the videos were analyzed using a scan sampling method. The motivation test was carried out in one of the replicates (9 hens in total) with outdoor access. To access the feed (used as gold standard) and to the outdoor area, hens had to push a transparent one-way door with increasing weight (100 g every two days). The test was interrupted when each hen did not pass through the door for two consecutive days. The motivational drive to access the two settings (i.e., feed and outdoor space) was quantified by constructing a behavioral demand function and calculating various indices based on economic theories. The number of visits per hen decreased when the door weight increased in both groups (P < 0.001). Nevertheless, while no hen reached the feed when the door weighed 650 g, hens opened the door up to a weight of 750 g to access the outside space. Reservation price (the maximum weight each hen pushed to access a specific resource) and total travel consumer surplus (the cumulative effort exerted by each hen during the test to reach a specific resource) averaged 445 g and 6.881 kg, respectively, without differences between resources. Moreover, the budget allocation was similar for feed and outdoor space. However, the demand for outdoor access resulted in a more inelastic trend than that for feed (P = 0.002), and the expenditure rate (the daily effort exerted by each hen during the test to reach a specific resource) was significantly higher for outdoor space as compared to feed (P < 0.001). In the group with access to an outdoor area, finally, the proportion of hens walking and self-grooming increased, while the proportion of hens resting decreased compared to the group kept indoors (P < 0.001). In conclusion, the present study demonstrates that laying hens are highly motivated to access outdoor space where they can find grass and other valuable resources and perform species-specific behaviors.