HPA-axis sensitivity

At 29 weeks of age, the reactivity of the HPA-axis was assessed by quantifying the corticosterone (CORT) response to restraint [41]. Birds were blood sampled from the wing veins and baseline samples were obtained within 3 min after the person entered their home pen. Immediately after this, each bird was placed in a large-meshed net hanging above the floor. The birds were blood sampled again at 10 min and 30 min after being placed into the bag and returned to the aviaries after the last sampling. Blood was collected with heparin-coated capillaries into eppendorf tubes, which were then centrifuged and the plasma was stored at −20°C until further analysis (see below).