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.

Modulating offspring responses: concerted effects of stress and immunogenic challenge in the parental generation.

The perception, processing and response to environmental challenges involves the activation of the immuno-neuroendocrine (INE) interplay. Concerted environmental challenges might induce trade-off when resource allocation to one trait occurs at the expense of another, also producing potential transgenerational effects in the offspring. We evaluated whether concerted challenges, in the form of an immune inoculum against inactivated Salmonella enteritidis (immune challenge, ICH) and a chronic heat stress (CHS) exposure on adult Japanese quail, modulate the INE responses of the parental generation and their offspring. Adults were inoculated and later exposed to a CHS along nine consecutive days. For the last 5 days of the CHS, eggs were collected for incubation. Chicks were identified according to their parental treatments and remained undisturbed. Induced inflammatory response, heterophil/lymphocyte (H/L) ratio and specific humoral response against sheep red blood cells (SRBC) were evaluated in both generations. Regardless of the ICH, stressed adults showed a reduced inflammatory response and an elevated H/L ratio compared with controls. In offspring, the inflammatory response was elevated and the specific SRBC antibody titres were diminished in those chicks prenatally exposed to CHS, regardless of the ICH. No differences were found in the H/L ratio of the offspring. Together, our results suggest that CHS exposure influences the INE interplay of adult quail, establishing trade-offs within their immune system. Moreover, CHS not only affected parental INE responses but also modulated their offspring INE responses, probably affecting their potential to respond to future challenges. The adaptability of the developmental programming of offspring would depend on the environment encountered.