This study was designed to characterize potential sexually dimorphic stress and immunological responses following a corticotropin-releasing hormone (CRH) challenge in beef cattle. Six female (heifers) and six male (bulls) Brahman calves (264 ± 12 d of age) were administered CRH intravenously (0.5 µg of CRH/kg body mass) after which serum concentrations of cortisol increased from 0.5 h to 4 h. From 1 h to 4 h after CRH administration, serum cortisol concentrations were greater in heifers than in bulls. In all cattle, increased serum concentrations of TNF-α, IL-6 and IFN-γ were observed from 2.5 h to 3 h after CRH, with greater concentrations of IFN-γ and IL-6 in heifers than bulls. Heifer total leukocyte counts decreased 1 h after CRH administration, while bull leukocyte counts and percent neutrophils decreased 2 h after CRH administration. Heifers had greater rectal temperatures than bulls, yet rectal temperatures did not change following administration of CRH. There was no effect of CRH administration on heart rate. However, bulls tended to have increased heart rate 2 h after CRH administration than before CRH. Heifer heart rate was greater than bulls throughout the study. These data demonstrate that acute CRH administration can elicit a pro-inflammatory response, and cattle exhibit a sexually dimorphic pro-inflammatory cytokine and cortisol response to acute CRH administration.
Keywords: Acute; CRH; cattle; cortisol; innate immunity; sexual dimorphism.