Biological Systems Engineering


First Advisor

Amy M. Schmidt

Date of this Version

Fall 12-2019


Zelt, Mara, "Persistence and Mitigation of Antibiotic Resistance in Manure and Manure-Amended Soils" (2019). Biological Systems Engineering--Dissertations, Theses, and Student Research


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: Agricultural and Biological Systems Engineering, Under the Supervision of Professor Amy M. Schmidt. Lincoln, Nebraska: December 2019

Copyright 2019 Mara Zelt


The emergence of antibiotic resistance (AR) is a growing global threat to human and animal health. The work described here asses the AR mitigation potential of management strategies at critical control points in livestock production, and agricultural land management as well as the effectiveness of a communication strategy to convey research-based information to empower behavioral change that could mitigate AR.

The first study evaluates the impact of beef cattle diet management strategies on AMR prevalence in manure. Two treatments – forage concentration and essential oils – in cattle diets were evaluated for their impact on AMR bacteria in feedlot manure. The second study documents the persistence of AR bacteria and AR genes in agricultural soil following fertilization by freshly scrapped beef feedlot manure, beef manure stockpiled for 6 months prior to application, composted beef manure, and inorganic fertilizer, to determine the risk of AR bacteria or gene transfer to crops fertilized by animal manures. This work also sought to assess the impact of social media outreach by a newly developed national extension team focused on AR education called iAMResponsible.

Results indicate that the inclusion of essential oil in cattle diet does not impact AR resistant populations in manure and that a conventional, low-forage finishing diet yields manure with an equal or reduced concentration of AR bacteria to cattle receiving higher levels of forage in their diet. The type of fertilizer applied had little or no lasting effect on the prevalence or concentration of AR bacteria or genes in agricultural soils. Social media outreach for the nationwide extension network iAMResponsible has proved effective for disseminating research-based information but should be paired with targeted programming for non-expert audiences. AR continues to be a source of concern for human and animal health; however, this work did not identify any reliable management methods for mitigating AR in animal environments or to significantly reduce any potential risk to human health or the environment posed by AR in animal manures.

Advisor: Amy M. Schmidt