CONICET | Buscador de Institutos y Recursos Humanos

The continued or repetitive exposure to stressors along time leads to a physiological state defined as chronic stress. This phenomenon affects different biological processes including the immune response, clearly impacting on the animals´ welfare. Avian species are endothermic and require comfortable temperatures for optimal development (22ºC- 24ºC). Consequently, heat stress is one of the main concerns in warm weather countries. The objective of this study was to analyse the effect of chronic heat stress and its recovery on cellular immune response in juvenile Japanese quail (Coturnix coturnix) females. One hundred and eighty quail were housed in 6 rearing pen boxes. Birds in 3 of the boxes were exposed to a temperature increase (from 24°C to 34ºC) during the lighting period throughout 9 days (Stress treatment). Birds in the other 3 boxes remained at 24°C during the whole study (Control treatment). Once stress protocol ended, subsequent 15 days were considered as the recovery period. Different sets of 6 birds per treatment were sampled at day 0 (basal), 3, 6, and 9 (heat stress), and at days 12, 15, 18, 21 and 24 (recovery). Percentage of inflammation and Heterophil/Lymphocyte (H/L) ratio were determined as cellular immune response variables. A two-way ANOVA showed an alteration in both cases in just 3 days of heat exposure and maximum effects on day 9. The percentage of inflammation recovered basal levels 6 days after heat exposure and H/L ratio required an extra 3 days. Results suggest differential modulation of immune variables with negative consequences after exposure to high temperatures. Findings are consistent with increased stress induced circulating mediators. Heat stress would represent an immune threat when sustained for 3 or more days therefore affecting animal welfare and fitness. However, cellular immune responses also appear resilient needing 6 to 9 days to recover basal levels

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