Tracing the development of the United States animal feed industry through the twentieth century, this dissertation analyzes the ways Americans have attempted to control various economic and ecological issues—from food insecurity to atmospheric pollution—through animal stomachs. Drawing from archival research and ethnographic fieldwork with farmers, scientists, feed companies, and cattle, I illustrate the academic partnerships, federal policies, and consumer politics that have formed this often-invisible animal feed-to-human food infrastructure. The emergence of this system dates back to the Progressive Era. At this time, scientists and policymakers worked to ensure the safety of feed and to enhance meat and milk production efficiency in cattle. Capitalizing on this new science, feed companies became important agricultural players as farmers increasingly relied on these businesses to chemically analyze feed mixes, provide standardized rations, and communicate the latest nutritional advice. Throughout the twentieth century, scientifically informed efforts to feed animals more efficiently encouraged the incorporation of different additives made from industrial byproducts. Reacting to fears of protein scarcity during the World War II era, experts focused on how ruminants could convert waste products from the plastic, pharmaceutical, and petroleum industries into human food. The limits of feeding chemical and agricultural waste to cattle came into question by the 1970s, as concerned scientists, farmers, and environmentalists attended to the consequences of industrial farming. Byproduct feeding led to nitrogen rich manure that polluted waterways. Antibiotic feeding led to concerns about bacteriological resistance. To mitigate the public-health and environmental problems created by mid-century feed efficiency efforts, academic and industrial experts developed new feed additives to help reduce the risks of antibiotic resistance and lower the production of methane by cattle. I argue that from around 1900 to 2019, experts continuously returned to the adaptability of ruminant animals to both transform inedible substances into desirable food and address larger economic and ecological problems.