Animal Science Department


Date of this Version



A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Animal Science (Meat Science and Muscle Biology), Under the Supervision of Professor Ty B. Schmidt. Lincoln, Nebraska: August, 2016

Copyright (c) 2016 Joe O. Buntyn


The objective of this study was to determine the metabolic, stress, hematology, organ weights, histology and cardiac anatomical features of beef heifers supplemented with zilpaterol hydrochloride (ZH) when exposed to a corticotropin-releasing hormone (CRH) and arginine vasopressin (VP) challenge. Crossbred heifers (n = 20; 556 ± 7 kg BW) were randomized into two treatment groups: 1) Control (CON): no ZH, and 2) Zilpaterol (ZIL): supplemented with ZH at 8.33 mg / kg (DM basis). The ZIL group was supplemented ZH for 20 d, with a 3-d withdrawal period. On d 24, heifers received an intravenous bolus of CRH (0.3 µg / kg BW) and VP (1.0 µg / kg BW). Blood samples were collected at 30- and 60-min intervals for serum, and 60-min intervals for plasma and whole blood, from -2 to 8 h relative to the challenge. Heifers were harvested to collect organ weights and histology samples on d 25, 26, and 27. There was a treatment (P < 0.001) effect for vaginal temperature (VT), with ZIL having a 0.1oC decrease in VT. A treatment x time effect (P = 0.002) was observed for non-esterified fatty acid such that concentrations were increased in CON heifers at 4, 6, 7, 7.5, and 8 hrs. There was a treatment effect for cortisol (P < 0.01) and epinephrine (P = 0.003) with ZIL having decreased concentrations. Glucose concentrations within the longissimus muscle were greater (P = 0.03) in CON heifers. Lactate concentrations and glycolytic potential within the biceps femoris were greater in CON heifers (P = 0.05). A treatment effect (P ≤ 0.02) was observed for calcium and potassium, with ZIL heifers having decreased concentrations. Zilpaterol heifers had increased concentrations of creatinine (P = 0.02). A treatment x time interaction (P = 0.02) was observed for phosphorus. Raw liver weights tended (P = 0.08) to be less in ZIL heifers. These data suggest some variations between treatments in terms of response to ZH supplementation and challenge; however, in the environmental conditions of this study, the data suggests that the supplementation of ZH does not negatively alter the status of homeostasis in cattle.

Advisor: Ty B. Schmidt