Let there be light: Artificial light cues improve early life ramp use of laying hen chicks in a commercial aviary.

In rearing aviaries, the provision of ramps has been found to facilitate the early utilization of elevated structures and increase inter-tier transitions. To maximize the welfare benefits associated with ramp use during early life, we investigated whether a moving light cue could increase early-life ramp use in laying hen chicks and subsequently improve bone biomechanical properties at a later age. The light cue was initially developed and tested in experimental settings, and this study aimed to validate the results from the experimental setting in a commercial setting. A total of 4800 Dekalb white birds were housed in eight pens (600 birds/pen) from one until 17 weeks of age (WoA) in a semi-commercial rearing barn. Ramps were provided in all pens, with half of the pens equipped with LED strips that provided intermittent light cues throughout the day (LED group), while the other half served as control pens without any light cues (CON). The number of inter-tier transitions and active use (e.g., walk/run, wing-assisted incline running) of ramps that did not result in a transition were recorded by scan sampling videos at multiple time points, when the cues were on as well as when they were off in LED pens. Same observation times were used in CON as well, although they did not have light cues. Additionally, bone biomechanical properties were assessed in tibiae and humeri collected from a subset of 160 birds (20 birds per pen) at 15 WoA. The analysis revealed that birds from the LED group exhibited more transitions and active use of ramps when the light cues were on compared to when they were off, as well as compared to the CON group (both cue-on and cue-off periods) throughout the observation period (until 10 WoA). No differences in bone biomechanical properties were observed between the CON and LED groups. These findings demonstrate that artificial light cues are suitable as a commercially viable tool to encourage vertical locomotion in laying hen chicks.