Age matters: Differential effects of the exposure to elevated environmental temperatures on representative variables of the immune system in juvenile and adult female Japanese quail.

Several days under the influence of high environmental temperature negatively impact on some immune-related variables of poultry species. However, it is little known whether this exposure affects differentially the immune response on different life stages. This study was aimed at characterizing the immune responses of juvenile and adult female Japanese quail (Coturnix coturnix) when exposed to a cyclic chronic heat stressor. Independent sets of juvenile (24) and adult (21) female Japanese quail were bred under thermoneutral conditions or exposed to an increasing temperature from 24 °C to 34 °C, for 8 h along nine consecutive days (chronic heat stressor). The inflammatory response against a mitogen, the antibody production against a non-pathogenic antigen and the heterophil to lymphocyte (H/L) ratio were measured after the ninth day of chronic heat exposure. Adult females had a more robust inflammatory response compared to their juvenile counterpart. The inflammatory response, the production of antibodies, and the H/L ratio were suppressed by the chronic heat stressor in the juvenile females; while in their adult counterpart, the production of antibodies was not affected by the chronic heat stress. Under the exposure of high environmental temperatures, juvenile females would be more susceptible to potentially harmful pathogens that require a robust immune response, while their adult counterparts would be able to mount an optimal acquired immune response against pathogens requiring this type of response. Our findings suggest that while heat stress during breeding should be avoided in both juvenile and adult females, more precautions should be taken during early life stages.