Abstract
Domestication is thought to increase stress tolerance. The connection between stressor exposure, glucocorticoids and behavioural responses has been studied in adults, where domestication effects are 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 (Gallus gallus), whereas others have found opposite results. Hence it remains unclear whether the HPA-axis is functional from hatch, and if domestication has affected the early post-hatch ontogeny of the stress response. Our aims were to investigate the early ontogeny of the HPA-axis and characterize behavioural and hormonal stress responses in ancestral Red Junglefowl and in two domestic layer strains. Plasma corticosteone and behavioural responses before and after physical restraint was measured on day one, nine, 16 and 23 post hatch. The results showed significant increases of corticosterone after stress in all three breeds at all the different ages. The HPA-response decreased with age and was lower in Red Junglefowl. Behavioural responses also decreased with age, and tended to be stronger in Red Junglefowl. In summary, the HPA-axis is reactive from day one, and domestication may have affected its development and reactivity, alongside with related behaviour responses.