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Title: The metabolic, stress axis, and hematology response of zilpaterol hydrochloride supplemented beef heifers when exposed to a dual corticotropin-releasing hormone and vasopressin challenge

item BUNTYN, JOE - University Of Nebraska
item Sanchez, Nicole
item SCHMIDT, TY - University Of Nebraska
item ERIKSON, G - University Of Nebraska
item SIEREN, SARA - University Of Nebraska
item JONES, STEVEN - University Of Nebraska
item Carroll, Jeffery - Jeff Carroll

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2016
Publication Date: 6/15/2016
Citation: Buntyn, J.O., Sanchez, N.C., Schmidt, T.B., Erikson, G.E., Sieren, S.E., Jones, S.J., Carroll, J.A. 2016. The metabolic, stress axis, and hematology response of zilpaterol hydrochloride supplemented beef heifers when exposed to a dual corticotropin-releasing hormone and vasopressin challenge. Journal of Animal Science. doi:10.2527/jas2015-0192.

Interpretive Summary: This research represents a collaborative effort of scientists from the University of Nebraska-Lincoln and the Livestock Issues Research Unit to determine the stress, immune and metabolic responses of calves supplemented or not with Zilpaterol Hydrochloride when the stress axis was exogenously activated. Zilpaterol Hydrochloride has been approved for use in the United States since 2007 (commercial name Zilmax®, Merck Animal Health, NJ, USA). Since gaining FDA approval, Zilpaterol Hydrochloride had become one of the most utilized beta adrenergic agonist for increasing lean muscle mass, dressing percentage and Gain:Feed efficiency in beef cattle. Currently there is limited literature available that describes the effects of Zilpaterol Hydrochloride supplementation in regards to cattle’s ability to manage stressors during the feeding of Zilpaterol Hydrochloride. Therefore, this study was designed to determine if differences exist in the manner that Zilpaterol Hydrochloride-supplemented cattle respond to a neurohormone-induced simulated stressor using exogenously-administered corticotropin-releasing hormone and vasopressin. Data from this study demonstrate that: 1) a simulated stress induced by administration of corticotropin-releasing-hormone and vasopressin in beef cattle elicits shifts in immune cell populations, 2) both stress hormones and immune cell responses are altered in beef heifers supplemented with Zilpaterol Hydrochloride when cattle are exposed to a simulated stress challenge, and 3) Zilpaterol Hydrochloride-supplemented animals are metabolically responsive to a simulated stress challenge. Some alterations in stress, hematology and metabolic variables were observed. However, within the controlled environment of this study, supplementation of Zilpaterol Hydrochloride did not appear to hinder finishing heifers ability to mount a response during a neurohomone-induced stimulated stress challenge. Furthermore, after an extensive review of literature, this study appears to be the first to document differences in hematology profiles in response to Zilpaterol Hydrochloride supplementation and a stress challenge in beef cattle. These data will be of interest to scientists in the field of stress physiology, as well as cattle producers.

Technical Abstract: The objective of this study was to determine the metabolic, stress, and hematology cell response of beef heifers supplemented with zilpaterol hydrochloride (ZH) when exposed to an endocrine stress challenge. Heifers (n = 20; 556 ± 7 kg BW) were randomized into two treatment groups: 1) Control (CON): no ZH supplementation, and 2) Zilpaterol (ZIL): supplemented with ZH at 8.33 mg/kg (DM basis). The ZIL group were supplemented ZH for 20 d, with a 3-d withdrawal period. On d 24, heifers received an i.v. bolus of corticotropin-releasing hormone (CRH; 0.3 µg/kg BW) and arginine vasopressin (VP; 1.0 µg/kg BW) to activate the stress axis. Blood samples were collected at 30-min intervals for serum, and 60-min intervals for plasma and whole blood, from -2 to 8 h relative to the challenge at 0 h (1000 h). Samples were analyzed for glucose, insulin, NEFA, blood urea nitrogen (BUN), cortisol, epinephrine, norepinephrine, and complete blood cell counts. Following the challenge, cattle were harvested over a 3-d period. Liver, longissimus muscle (LM), and Biceps femoris (BF) samples were collected and analyzed for glucose, lactate, and glycolytic potential (GP). There was a treatment (P < 0.001) effect for vaginal temperature (VT), with ZIL having a 0.1oC decrease in VT when compared with CON. A treatment x time effect (P = 0.002) was observed for NEFA. A treatment effect was observed for BUN; ZIL had decreased BUN concentrations compared with CON (P < 0.001) prior to the challenge; however, no treatment x time effect was observed. There was also a treatment effect for cortisol (P < 0.01) and epinephrine (P = 0.003); ZIL had decreased cortisol and epinephrine during the CRH/VP challenge, when compared with CON. There was a time effect for total white blood cells, lymphocytes, and monocytes; each variable increased (P < 0.01) 2 h post-challenge. Additionally, neutrophil counts decreased (P < 0.01) in response to CRH/VP challenge in both treatment groups. Glucose concentrations within the LM were greater (P = 0.03) in CON when compared with ZIL. Lactate concentrations and GP within the BF were greater in CON (P = 0.05) when compared with ZIL. These data suggest there are some variations observed between treatments in terms of response to the CRH/VP challenge; however, in the environmental conditions of this trial, none of the variations observed suggests that the supplementation of ZH detrimentally alters the ability of cattle to effectively respond to stressful stimuli.