Relationship between hair cortisol and plasma heat shock proteins in response to heat stress in resilient and sensitive cattle breeds

The understanding of the physiological mechanisms of response to heat-stress in different phenotypes is a key feature to future breeding programs that increase cattle breeds resilience to cope with climate change. Cortisol and Heat Shock Proteins release are hallmarks of heat stress response, however the relationship between these three parameters is poorly studied in cattle. This study evaluated the relationship between cortisol and plasma HSP concentrations in response to increased Temperature-Humidity-Index in different phenotypes to identify specific indicators of heat stress. In this study, native breeds activated specific heat loss strategies despite no increment in cortisol levels, calling into question its use as a measure of heat-stress in historically adapted breeds. Plasma HSP60 and HSP90 reveal a specific pattern through an interaction with THI and cortisol, ended to be breed specific indicators for Alentejana and Mertolenga respectively. Plasma HSP70 concentrations, although highly correlated with THI, were independent of cortisol release in all phenotypes, thus, indicating that this protein is a marker of environmental heat exposure rather than a marker of heat-stress. Studies on the adaptive mechanisms governing heat-stress tolerance, are of paramount relevance for the selection of resilient cattle and the profitability of livestock under a scenario of global warming.