When a domestic chicken, or its ancestor, the Red Junglefowl, faces a threatening situation, they trigger a stress response aimed at stimulating the flight response or fighting against the threat. However, it could be possible that during the first days of age, the stress response is not fully matured, and therefore, the bird might be less perceptive or responsive to threats coming from its surroundings. Considering that a commercial environment might be potentially stressful for newly hatched chicks, the authors were motivated to answer if chickens are responsive to a threatening situation during the first days of age and if the domestication process, which they have undergone, had an impact on the stress response. 

To answer the question, four groups of domestic chickens, and four groups of Red Junglefowl were tested before and after they were exposed to a stressful situation. The birds were rapidly moved inside a bag, spending less than ten minutes trapped in this situation. As an indicator of the stress response, the hormone corticosterone was measured, using blood samples. It is important to bear in mind that the higher the values of this hormone in the blood stream, the more stressed a bird is. The stress response was measured at four sampling points: one, nine, sixteen and twenty-three day(s) after hatch. For each point, a group of chickens and a group of the ancestral species, reared under the same breeding conditions, were evaluated.  

One day after hatch and without experiencing the unpleasant stressor, the Red Junglefowl had lower levels of the hormone mediating the stress response. When put in a bag, chickens and junglefowl responded to the unpleasant situation at all ages. In particular, on day one, even though all birds activated their stress response (as the levels of the hormone increased), the response of the junglefowl chicks was not as powerful as that of the domestic chicks. As the birds grew older, the stress response was still there but not as strong as one day after hatching.  

With this study, the authors answered the question that drove their research: one-day old chicks are able to respond to a threating situation coming from their surroundings. Interestingly, the intensity of the response was different between the domestic chickens and their ancestor. The domestic chickens triggered a stronger stress response after an unpleasant event one day after hatch. In terms of aging, the system in charge of the stress response matures, keeping the ability to respond to a stressor, but not being as intense as day one after hatch. The maturation of the stress response also reduces the difference between the chicken and its ancestor.  

The development of a young chick can be shaped by an exposure to a threatening event during the first days of life. The authors showed that thousands of years of domestication have had an impact on the stress response of the chicken, raising awareness on the importance of controlling potentially stressful situations so as to maintain animal welfare standards in productive environments.  

REFERENCES. 

Ericsson, M. and Jensen, P. (2016) Domestication and ontogeny effects on the stress response in young chickens (Gallus gallus). Scientific Reports.  6, 35818.