Influence of genetics and light during incubation on stress responsivity in young laying hens

Light during incubation is a promising intervention to improve chicken welfare. More specifically, a cycle of alternating green light and darkness reduces fearfulness in poultry. However, this has mainly been shown in studies of broiler chicks, whereas the impact on laying hens is unknown. As the developmental stage has a major impact on the ability to cope with stressors at adulthood, we investigated the effects of light during incubation on the stress sensitivity of pullets of two common layer hybrids: ISA Brown and Dekalb White. In addition, to fully comprehend their stress responsivity in both experimental settings and in their home-pens, we tested a new video tracking system on control laying hens in their home-pen in pilot studies. For the main research, half of the eggs were incubated in standard darkness and the other half in a green light:dark cycle of L12:D12 throughout incubation, resulting in a 2*2 design. Animals were reared in 20 pens of non-mixed treatments, and individual behavioural measurements were performed to compare experimental treatments on the pullets’ stress responsivity. In parallel, the video tracking system was tested on control laying hens, using ArUco codes for identification of each bird, and monitoring their location and direction in both day and night situations. A cox model was used to determine effects of incubation, hybrid and their interaction. Testing revealed an effect of genetic background and a tendency of light during incubation in a voluntary approach test. ISA Browns pecked at the food offered by a human faster than Dekalb Whites (N = 189, p < 1,84e 05), and within each hybrid, light-incubated pullets tended to peck at the food faster than dark-incubated ones (p = 0,0981). The relevance of human-pullet interactions to poultry farming makes these results promising in terms of improving chicken welfare by reducing their fear of humans. Finally, the pilots revealed both location and direction of identified individuals can be tracked from as early as 7 weeks old. The system will be implemented in the next batch to further highlight the effects of light during incubation and genetic background on stress responsivity in pullets, for example by monitoring their perch use or their behaviour synchronisation level, important for this highly-social species. Light being an easy adjustment to bring to hatcheries, the results from our next batch will tell whether implementing a lighted incubation system in the industry can improve laying hen welfare significantly.