Incubation and hatching conditions of laying hen chicks explain a large part of the stress effects from commercial large-scale hatcheries

In commercial egg production, laying hen chicks are exposed to several stressful events during incubation, hatching, and their first hours in life. We have previously shown that hatching and processing are associated with increased corticosterone concentration and further affect behavior and stress sensitivity in a short- as well as long-term perspective. However, it is not known whether these long-term stress effects are caused by the hatchery processing (sex sorting, vaccination, conveying, and loading for transport) or if they are mainly caused by potentially stressful events before processing, during incubation and hatching. In the present study, the aim was to assess the effects of incubation and hatching only, compared to stress effects from the entire hatchery processing. We compared Lohmann LSL chicks incubated, hatched, and processed in a commercial hatchery with chicks incubated and hatched at the same time but not further processed. We studied behavior in a novel arena and during tonic immobility, as well as weight development and corticosterone reaction during a stress challenge. Processed chicks had poorer weight development and were more active in the novel arena test. However, there were no significant differences between the groups in corticosterone reactivity or tonic immobility. When comparing with previous data, both groups had elevated corticosterone concentrations compared to what we had previously reported from chicks hatched under calm and non-stressful conditions. In conclusion, incubation and hatching alone caused long-term stress effects in chickens, but further processing exacerbated these effects to some extent.