Domestication effects on behavioural and hormonal responses to acute stress in chickens.

Comparative studies have shown that alterations in physiology, morphology and behaviour have arisen due to the domestication. A driving factor behind many of the changes could be a shift in stress responses, with modified endocrine and behavioural profiles. In the present study we compared two breeds of chicken (Gallus gallus), the domestic White Leghorn (WL) egg laying breed and its ancestor, the Red Junglefowl (RJF). Birds were exposed to an acute stress event, invoked by 3 or 10 min of physical restraint. They were then continuously monitored for the effects on a wide range of behaviours during a 60 min recovery phase. Blood samples were collected from the chicken at baseline, and after 10 and 60 min following a similar restraint stress, and the samples were analyzed for nine endogenous steroids of the HPA and HPG axes. Concentration of the steroids was determined using validated liquid chromatography tandem mass spectrometry methods. In RJF, an immediate behavioural response was observed after release from restraint in several behaviours, with a relatively fast return to baseline within 1h. In WL, some behaviours were affected for a longer period of time, and others not at all. Concentrations of corticosterone increased more in RJF, but returned faster to baseline compared to WL. A range of baseline levels for HPG-related steroids differed between the breeds, and they were generally more affected by the stress in WL than in RJF. In conclusion, RJF reacted stronger both behaviourally and physiologically to the restraint stress, but also recovered faster. This would appear to be adaptive under natural conditions, whereas the stress recovery of domesticated birds has been altered by domestication and breeding for increased reproductive output.