Domestication and ontogeny effects on the stress response inyoung chickens (Gallus gallus)

Domestication is thought to increase stress tolerance. The connection between stressor exposure,glucocorticoids and behavioural responses has been studied in adults, where domestication effectsare evident. Early stress exposure may induce detrimental effects both in short-and long term.Previous research has reported a lack of glucocorticoid response in newly hatched chickens (Gallusgallus), whereas others have found opposite results. Hence it remains unclear whether the HPA-axis isfunctional from hatch, and if domestication has affected the early post-hatch ontogeny of the stressresponse. Our aims were to investigate the early ontogeny of the HPA-axis and characterize behaviouraland hormonal stress responses in ancestral Red Junglefowl and in two domestic layer strains. Plasmacorticosteone and behavioural responses before and after physical restraint was measured on dayone, nine, 16 and 23 post hatch. The results showed significant increases of corticosterone after stressin all three breeds at all the different ages. The HPA-response decreased with age and was lower inRed Junglefowl. Behavioural responses also decreased with age, and tended to be stronger in RedJunglefowl. In summary, the HPA-axis is reactive from day one, and domestication may have affectedits development and reactivity, alongside with related behaviour responses.Funding agencies: Swedish Research Council (VR); Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS); European Research Council (ERC) [Genewell 322206]</p