Response to adrenocorticotropic hormone or corticotrophin releasing hormone and vasopressin in lactating cows fed an immune-modulatory supplement under thermoneutral or acute heat stress conditions

Authors: MCBRIDE, M - University Of Arizona; Sanchez, Nicole; Carroll, Jeffery - Jeff Carroll; Broadway, Paul; ORTIZ, X - University Of Arizona; COLLIER, JAYNE - University Of Arizona; CHAPMAN, JIM - Phibro Animal Health Corporation; MCLEAN, DEREK - Phibro Animal Health Corporation; KATTESH, HANK - University Of Tennessee; GILLESPIE, B - University Of Tennessee; XIAO, Y - University Of Arizona; COLLIER, ROBERT - University Of Arizona

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2020
Publication Date: 4/16/2020
Citation: McBride, M.L., Sanchez, N.C., Carroll, J.A., Broadway, P.R., Ortiz, X.A., Collier, J.L., Chapman, J.D., Mclean, D.J., Kattesh, H.G., Gillespie, B.E., Xiao, Y., Collier, R.J. 2020. Response to adrenocorticotropic hormone or corticotrophin releasing hormone and vasopressin in lactating cows fed an immune-modulatory supplement under thermoneutral or acute heat stress conditions. Journal of Dairy Science. 103(7):6612-6626. https://doi.org/10.3168/jds.2019-17548.
DOI: https://doi.org/10.3168/jds.2019-17548

Interpretive Summary: Heat stress is a significant problem for the dairy cattle industry, leading to losses in production, and also compromising immune function. OmniGen-AF is an immune stimulant that may influence immune responses. Additionally, there is evidence that this product may mitigate some of the negative effects associated with heat stress. Therefore, a study was conducted with scientists from the University of Arizona, the USDA-ARS Livestock Issues Research Unit, the University of Tennessee and Phibro Animal Health Corp. to determine whether OmniGen altered the stress response of dairy cows fed OmniGen and exposed to heat stress. Data from this study indicate that dairy cows fed OmniGen had a reduced stress response to heat stress as well as to simulated stress challenges administered when cows were housed in thermal neutral or heat stress environments. Ultimately, these data provide information on a possible supplement to reduce the burden of heat stress in lactating dairy cows. Information from this study is of value to producers in the dairy industry as well as scientist in the field of stress physiology, and veterinarians.

Technical Abstract: Adrenal responsiveness was tested in lactating Holstein dairy cows fed OmniGen-AF® (OG), an immune stimulant feed additive and compared to control (CON) cows that ingested feed without the additive using bolus injections of a combination of corticotropin releasing hormone (CRH, 0.3 µg/kg BW) ) and arginine vasopressin (VP, 1.0 µg/kg BW) or adrenocorticotropic hormone (ACTH, 0.1 IU/kg BW) and subjected to two different temperature environments: thermoneutral (TN; temperature humidity index (THI)<68) for 24 h/d) and heat stress (HS; THI>68 12 h/d). Cows (506) were initially fed OG (n=254) or CON (n=252) diets for 44d of the study. A subgroup of cows (n=12, 6 OG 6 CON) were then transported to and housed in 2 environmentally controlled rooms where they underwent 10 days each of TN then HS conditions. The animals were challenged with CRH-VP on d6 of TN (d53 of study) and on d1 of HS (d56 of study) and with ACTH on d7 of TN (d 54 of study) and on d2 of HS (d57 of study). Infusion of the synthetic hormones took place at 1000 (0 hr.) on each challenge day. Blood samples were taken in 30 min intervals and first collected at 0800 (-2hr) and drawn until 1800 (8hr). Prior to challenge, serum progesterone was elevated in OG fed animals compared to CON. Infusion of releasing factors (CRH-VP or ACTH) caused increases in serum cortisol and progesterone but cortisol release was higher in CON versus OG while progesterone was lower in CON compared to OG fed animals. Serum ACTH increased following infusion of both releasing factor's but this increase was greater following CRH-VP than ACTH infusion. The mean ACTH increase was also lower in OG-fed animals. Serum bovine corticosteroid-binding globulin (bCBG) also increased following infusion of releasing factors in both groups but free cortisol index (FCI) was still lower in OG-fed animals. Increases in serum cortisol induced elevations of serum glucose, NEFA and insulin concentrations and these responses tended to be reduced in OG-fed animals. Heat stress enhanced the adrenal response to releasing factors in CON but not in OG fed animals. Collectively, these data suggest that OG supplementation reduced the effects of heat stress on lactating Holstein dairy cows in part by reducing adrenal responsiveness to factors regulating cortisol release. This was associated with a reduced ACTH concentration and an increase in adrenal progesterone release following infusion of the releasing factors in OG-fed animals.