August 3, 2026

The inside story of the discovery and development of monensin, a feed additive that changed the beef industry

A new Perspective and Commentary in Applied Animal Science recounts the 50-year history of monensin, from a redirected research project to a product now used in 90% of US feedlot cattle

Champaign, IL, August 3, 2026---Fifty years ago, the feed additive monensin was approved for use in beef cattle and quickly transformed how cattle are fed in the United States and around the world. Now, a new Invited Perspective and Commentary article published in Applied Animal Science tells the story of that discovery from the people who lived it. Written by Arthur (Art) Raun, Leo Richardson, and Emerson Potter, three retired Eli Lilly & Co. (Lilly) scientists who were central to the work, the article traces monensin’s path from a redirected research program with limited resources to one of the most widely used products in animal agriculture.

“The discovery of monensin’s usefulness in cattle was not the result of serendipity, but the result of a designed program that hit several struggles along the way,” explained corresponding author Art Raun, PAS, who led the ruminant research effort at Lilly. “We set out to do two things that had never been done before: build a test system that could find compounds to change how the rumen produces volatile fatty acids, and then determine whether those changes would actually improve feed efficiency. Before monensin, the only practical way to shift that balance was to change the animal’s ration.”

The authors describe how the program was built after a previous approach was redirected entirely, and the team worked to hone in on the pathways to finding a significant new product that could move the needle in ruminant production. They determined that the most realistic chance of success was in improving rumen energy efficiency and landing on a shared goal of increasing production of propionic acid in the rumen at the expense of acetic and butyric acids, a shift that would recover more energy from feed.

To find out what would be needed to induce this shift, the team developed an in vitro rumen screen (a critical step that was very nearly prevented because of budget concerns), allowing the team to test several thousand synthetic and fermentation compounds until they found a winner. The article recounts the pivotal moment in June 1970 when a laboratory technician noticed that one fermentation compound had boosted propionic acid production so dramatically that its reading ran off the graph paper. That compound was monensin.

As the authors note, this discovery was especially fortuitous because monensin had already been identified as a biologically active compound in 1967 and was approved by the US Food and Drug Administration (FDA) for controlling coccidiosis in poultry, meaning much of the groundwork on safety, formulation, and residue testing had already been done.

Once the compound’s activity was recognized, a multidisciplinary team moved quickly through the studies required for approval, from dose-titration trials and carcass evaluations to tissue residue, toxicology, and environmental safety work. Just five years and five months passed between the first sign of monensin’s activity in the rumen screen and its FDA approval for feedlot cattle.

Monensin was introduced to the market in January 1976 and reached an astounding roughly 90% adoption in the feedlot market within just a few months, a level it has held ever since. Today it is also fed to 70% of US dairy cows, is approved in 26 countries, and has been the subject of tens of thousands of scientific papers and technical reports. Beyond improving feed efficiency, the authors note that monensin is credited with moderating feed intake and rumen digestion, reducing digestive disorders, and lowering methane emissions from cattle.

Bill Weiss, PhD, PAS, Dipl. ACAS, editor in chief of Applied Animal Science, commented on the article. “Monensin is fed to most of the cattle raised in the United States and is widely used in numerous other countries. This Perspective and Commentary article is an interesting history lesson of the research program that led to its development, written by three of the lead investigators of the project.”

The authors conclude that monensin’s development stands as an example of how a focused research program, built on a clear mechanism of action and sustained through both corporate review and close collaboration with the academic community, can deliver lasting value to a company, its customers, and the industry as a whole. The worldwide economic impact of monensin in feed savings for beef feedlot cattle alone, not counting its many other applications, is estimated to exceed $23 billion.

The article appears in the August 2026 issue of Applied Animal Science.

Notes for editors
“Invited Perspective and Commentary: History of the discovery and 50-year development of monensin for beef cattle,” by Arthur P. Raun, Leo F. Richardson, and Emerson L. Potter (https://doi.org/10.15232/aas.2026-02797), Applied Animal Science, volume 42, issue 4 (August 2026), published by FASS and Elsevier.

This article is openly available at https://doi.org/10.15232/aas.2026-02797.

To schedule an interview with the author(s), please contact Art Raun at enaranch@aol.com.

About Applied Animal Science
Applied Animal Science (AAS) is a gold open access, peer-reviewed scientific journal and the official publication of the American Registry of Professional Animal Scientists (ARPAS). In continuous publication since 1985, AAS is a leading outlet for animal science research. It has a Journal Impact Factor and is indexed by Scopus, Clarivate, CABI, and AGRICOLA. AAS caters to a wide and comprehensive audience, and its readers are typically university, extension, animal-industry, and government employees; members of professional societies and related organizations; producers, commodity organizations, and related feed and foods industries; researchers and students; and consultants and companies providing products and services in animal agriculture. The journal welcomes novel manuscripts on applied technology, reviews on the use or application of research-based information on animal agriculture, commentaries on contemporary issues, short communications, and technical notes. Topics that will be considered for publication include (but are not limited to) feed science, farm animal management and production, dairy science, meat science, animal nutrition, reproduction, animal physiology and behavior, disease control and prevention, microbiology, agricultural economics, and environmental issues related to agriculture. Themed special issues also will be considered for publication. www.appliedanimalscience.org

About the American Registry of Professional Animal Scientists (ARPAS)
The American Registry of Professional Animal Scientists (ARPAS) is the organization that provides certification of animal scientists through examination, continuing education, and commitment to a code of ethics. Continual improvement of individual members is catalyzed through publications (including the AAS journal) and by providing information on educational opportunities. ARPAS is affiliated with five professional societies: American Dairy Science Association, American Meat Science Association, American Society of Animal Science, Equine Science Society, and Poultry Science Association. www.arpas.org

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FASS, the services division of the American Dairy Science Association, provides management services to nonprofit associations and societies with a mutual interest in supporting the advancement of animal agriculture and food systems through research and education. We support nonprofits by providing services for accounting, membership management, convention and meeting planning, information technology, and scientific publishing. The FASS publications department provides journal management, peer-review support, copyediting, composition, and proofreading; the staff includes several BELS-certified (www.bels.org) technical editors and experienced composition staff. www.fass.org

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