|Hulbert, Lindsey -|
|Ballou, Michael -|
|Caldwell, Lisa -|
|Loyd, Andrea -|
|Vann, Rhonda -|
|Welsh Jr, Thomas -|
|Randel, Roanld -|
Submitted to: Journal of Innate Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 28, 2012
Publication Date: July 15, 2013
Citation: Hulbert, L.E., Carroll, J.A., Ballou, M.A., Sanchez, N.C., Dailey, J.W., Caldwell, L.C., Loyd, A.N., Vann, R.C., Welsh Jr, T.H., Randel, R.D. 2013. Sexually dimorphic stress and innate immunological responses of Brahman cattle following an intravenous corticotropin-releasing hormone (CRH) challenge. Journal of Innate Immunity. 19:378-387. Interpretive Summary: This study was a collaborative effort between scientists from Texas AgriLife Research, the Livestock Issues Research Unit, Mississippi State University, and Texas Tech University to determine if sexually dimorphic responses exist in cattle when administred a corticotrophin-releasing hormone challenge. Stressful events such as handling, weaning, and commingling of unfamiliar cattle are associated with decreased performance and increased morbidity and mortality. However, not all stressors negatively affect the immune system. There is evidence that acute stressors, or stressors that occur over a short period of time, can actually prime the immune response and enhance subsequent responses. Additionally, stress responses have been demonstrated to be affected by sex, in which females have greater circulating concentrations of the stress hormone cortisol compared to males. Therefore, a study was designed to determine the influence of sex on the physiological, endocrine, and immune responses of heifers and bulls to a corticotrophin-releasing hormone challenge. The results from this study suggest that acute stimulation of the stress response using corticotrophin-releasing hormones can stimulate the stress and immune responses, resulting in a sexually dimorphic response. Specifically, heifers produced a greater increase in cortisol in response ot corticotrophin-releasing hormone than bulls. Additionally, heifers produced a greater increase in the pro-inflammatory cytokines interleukin-6 and interferon-gamma than bulls. These data demonstrate that heifers may be less responsive to cortisol than bull calves, resulting in the production of greater concentrations of pro-inflammatory cytokines in response to acute stimulation with corticotrophin-releasing hormone. These results will be of interest to scientists in the field of stress and immune physiology, as well as beef cattle producers, and can be used in order to change management practices in order to enhance performance and decrease the potential negative effects of stressors on beef calves production.
Technical Abstract: This study was designed to characterize potential sexually dimorphic stress and immunological responses following corticotrophin-releasing hormone (CRH) challenge. Six female (heifers) and five male (bulls) Brahman calves (264 ± 12 days of age) were challenged with 0.5 micrograms of CRH/kg body weight. Following CRH administration, cattle displayed an increase in cortisol from 0.5 to 4 hour. Heifer cortisol concentrations were greater at 1 to 4 hours than bulls. Heart rate did not change following CRH administration. However, bulls tended to have elevated heart rates 2 hour after CRH administration. Heifer heart rate was greater than bulls throughout the study. Likewise, heifers had greater rectal temperatures than bulls, yet rectal temperatures did not change following administration of CRH. Increases in serum concentration of tumor necrosis factor-alpha, interleukin-6, and interferon-gamma were observed at 2.5 to 3 hours following CRH administration, with heifers exhibiting greater concentrations of interferon-gamma and interleukin-6 than bulls. Heifer total leukocyte counts decreased 1 hour after CRH administration, while bull leukocyte counts and neutrophil percentages decreased at 2 hours. These data demonstrate that acute CRH administration can elicit a pro-inflammatory response, and cattle exhibit a sexually dimorphic innate immune and cortisol response to acute CRH administration.