Animal Science Department


First Advisor

Jessica Lynn Petersen

Date of this Version



Duffy, E.M. (2019). Impact of Beta-Adrenergic Agonist Supplementation and Heat Stress on the Microbiome and Gastrointestinal Transcriptome of Sheep. (Master's thesis). University of Nebraska, Lincoln, NE.


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Animal Science, Under the Supervision of Professor Jessica Lynn Petersen. Lincoln, Nebraska: August, 2019.

Copyright (c) 2019 Erin Margaret Duffy


Improving animal growth and efficiency are critical points of research as the world’s population and demand for agriculture products increase. Therefore, adaptions or changes in the gut are of interest to maximize growth efficiency and wellbeing of livestock. The gastrointestinal tract of the rumen plays many critical roles with the assistance of the associated microbial community. One way to improve animal performance is supplementation of β-adrenergic agonists (β-AA) which are commonly fed to cattle during the last 20-40 days of the finishing period, improving muscle growth by decreasing adipose deposition and increasing muscle accretion. Two β-AA, Ractopamine HCl (β1-AA) and Zilpaterol HCl (β2-AA) are currently approved for use in beef cattle in the United States. Alternatively to the beneficial effects of β-AA, heat stress in livestock decreases production efficiency and growth. Based on anecdotal reports it has been suggested that supplementation of β-AA could potentially exacerbate the stress response caused by hyperthermia leading to increased mortality. However, little research has been conducted to investigate the interaction between these two factors. Therefore, the purpose of these studies was to investigate the impact of heat stress, β-AA and the interaction between the two with respect to the ruminant gastrointestinal tract. Microbial communities were isolated from rumen and cecum contents and RNA was isolated from rumen epithelium of lambs supplemented Zilpaterol HCl and Ractopamine HCl housed in either an ambient or heat stressed environment for 21 d. Additionally RNA was isolated from rumen epithelium of lambs supplemented Ractopamine HCl housed in either an ambient or heat stressed environment for 30 d. No interaction was found between β-AA and heat stress in either the microbial community or RNA studies. Heat stress and β-AA supplementation changed the composition of particular taxa in the rumen microbiome, while the addition of ammonium chloride to the second group significantly impacted the cecal microbial composition. Additionally, heat stress, but not β-AA supplementation, impacted the transcriptome profile of the rumen epithelium by upregulating the oxidative stress response. Based on these results, we conclude that β-AA do not induce an increased stress response within the ruminant gastrointestinal tract.

Advisor: Jessica L. Petersen