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

This study evaluated the relationship between cortisol and Heat Shock Proteins (HSP) release, and heat stress (HS) induced by high Temperature-Humidity-Index (THI) in cattle. Cows of heat-tolerant (Alentejana, ALT; Mertolenga, MERT) and heat-sensitive (Holstein-Frisian, HF) Bos taurus breeds, calving in August and January, were sampled at 39 ± 5 days postpartum at the end of Summer and Winter. For each cow, the THI of the previous 60 days (THI60) was calculated, ocular, vaginal and rectal temperatures were measured, blood was collected for BHB, total T3 and T4, HSP60, HSP70 and HSP90 assays, and neck hair was collected for measurement of cortisol concentrations (HCC). Plasma HSP60 concentrations were decreased by the independent increase in THI60 and HCC, but in ALT cows the simultaneous THI60 and HCC increase had the opposite effect. Plasma HSP70 concentrations were not related to HCC, but were increased by increased THI60 only in ALT and MERT cows. Plasma HSP90 concentrations were decreased by the independent increase in THI60 and HCC in ALT and HF cows, but in MERT cows the HSP90 decrease was only accomplished when in presence of the simultaneous increase in THI60 and HCC. In conclusion, significant breed-specific phenotypes of response to HS were identified.