Influence of light exposure during late incubation, early feeding, and litter access posthatch on the stress response and body weight gain in laying hen chicks

In-ovo sexing opens the door to on-farm hatching in the laying hen sector, but knowledge on the implications of different hatching system factors remains limited. This study addressed the influence of continuous light exposure during the last three days of incubation, post-hatch feed and water access, and post-hatch litter access on stress responsivity and body weight gain in laying hen chicks. Through a pilot experiment and two replicated experiments, we investigated the influence of these factors on physiological stress responsivity and body weight gain up to eight weeks of age. Short-term stress responsivity was evaluated by serum corticosterone and cloacal temperatures during processing procedures (e.g., sexing, sorting, vaccinating). Additionally, cumulative stress responsivity until eight weeks of age was assessed through corticosterone analysis in feather samples, and chick weights were recorded throughout. The presence of continuous lighting during the last three days of incubation affected stress responsivity, potentially by disrupting the circadian release of melatonin and thus corticosterone secretion. Immediate access to post-hatch feed and water affected serum corticosterone levels, indicating a relationship between early feeding and stress responsivity. However, the underlying mechanisms remain unclear. Post-hatch feed and water access did not have long-term effects on body weight gain, as fully deprived chicks were able to catch up within a day. Despite our study's exploratory nature, a complex relationship between stress responsivity and the hatching environment was shown, highlighting the need for future research to focus on disentangling and optimizing hatching system factors to minimize early life stress.