Effect of Accelerated Adaptation Programs on Feedlot Performance and Health of Steers Drenched with Megasphaera elsdenii and Quantifying and Partitioning Multi-year Carbon Dioxide and Methane Fluxes in a Grazed Temperate Pasture

Authors

• Rebecca McDermott, University of Nebraska-LincolnFollow

First Advisor

Galen Erickson

Degree Name

Doctor of Philosophy (Ph.D.)

Committee Members

Andy Suyker, George Burba, Jim McDonald, Yijie Xiong

Department

Animal Science

Date of this Version

5-6-2026

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree Doctor of Philosophy

Major: Animal Science

Under the supervision of Professor Galen Erickson

Lincoln, Nebraska, May 2026

Comments

Copyright 2026, Lester Ray Miller. Used by permission

Abstract

With strong consumer demand for beef and increasing concern about the environmental impacts of beef production, improving production efficiency and advancing the understanding of the environmental footprint are critical for the long-term sustainability of beef production systems. The first experiment evaluated the effect of accelerated adaptation strategies, using energy intake and cattle behavior, on feedlot performance, carcass characteristics, and health of yearling steers drenched with exogenous Megasphaera elsdenii. Accelerated adaptation programs (0, 7, or 14 d transition to 100% finisher) were compared to a traditional 21-d adaptation. Dry matter intake responded quadratically across treatments, with the greatest intake observed in the traditional 21-d program and the lowest intake in the 7-d adaptation. Average daily gain and hot carcass weight also exhibited quadratic responses, with cattle assigned to the traditional and 0-d accelerated adaptation treatments achieving greater gains and hot carcass weights than those in the 7- and 14-d programs. These results indicate that steers administered Megasphaera elsdenii can be transitioned to 100% finisher within 2 d without compromising feedlot performance, carcass characteristics, or health.

The second experiment quantified and partitioned carbon dioxide (CO₂) and methane (CH₄) fluxes in a continuously grazed smooth bromegrass pasture using eddy covariance, static chambers, and animal positioning data. Over an eight-year period, net ecosystem exchange exhibited substantial interannual variability driven by differences in precipitation and subsequent forage productivity. The pasture ecosystem functioned as a carbon sink or near neutral for the first four years but became a carbon source in the following four years, resulting in a cumulative net ecosystem exchange of 650 g C m^-2. Chamber measurements indicated that soils consistently functioned as a small CH₄ sink, whereas eddy covariance measurements reflected CH4 emissions influenced by cattle within the flux footprint. Average enteric CH4 production was 164 g hd⁻¹ d⁻¹, consistent with published values. However, average CO₂ emissions from cattle respiration (3,606 g hd⁻¹ d⁻¹) were substantially lower than model predictions. These results demonstrate that grazed pastures can shift between carbon sink and source states, emphasizing the need for long-term measurements. Continuous, high-resolution animal positioning data are also essential for accurately partitioning CO₂ and CH₄ fluxes.

Recommended Citation

McDermott, Rebecca, "Effect of Accelerated Adaptation Programs on Feedlot Performance and Health of Steers Drenched with Megasphaera elsdenii and Quantifying and Partitioning Multi-year Carbon Dioxide and Methane Fluxes in a Grazed Temperate Pasture" (2026). Dissertations and Doctoral Documents, University of Nebraska-Lincoln, 2023–. 476.
https://digitalcommons.unl.edu/dissunl/476