Stress responses in neonatal meat and layer Nagoya chicks

We reported that meat chicks have either a greater capability to acclimatize to novel environments, or a blunted hypothalamic-pituitary-adrenal response to novel environments compared with layer chicks in a commercial base. The present study compared the differences in behavior and plasma corticosterone concentrations under isolation-induced stress between neonatal meat and layer Nagoya chicks which had been separated from the same population. Both types of neonatal chicks reared in groups were individually separated and their spontaneous activity and distress-induced vocalizations were monitored for 10 min. The responses of the two types were remarkably different, with the meat chicks being less active than the layer chicks. Distress-induced vocalizations were fewer in the meat than in the layer chicks. The meat chicks spent more time in a sleeping posture during isolation-induced stress. Plasma corticosterone concentrations measured at the end of the test tended to be higher in the layer chicks than in meat ones, but not significantly. In conclusion, the selection of Nagoya chickens for meat and layer may have trends similar to those observed in commercial chickens in relation to stress susceptibility.