Factory farming has been around for roughly a century, with its roots in the 1920s United States. What started as one woman’s accidental chicken order in 1923 grew into an industrial system that now produces an estimated 99% of all livestock in the U.S. and 74% of land livestock worldwide. The transformation didn’t happen overnight. It unfolded in stages across several decades, driven by new technology, cheap grain, and growing consumer demand for affordable meat.
The Accidental Start: Chickens in the 1920s
Before the 1920s, chickens were barnyard animals kept mainly for eggs. Nobody raised them specifically for meat on a commercial scale. That changed in 1923 when Cecile Steele, a housewife in Ocean View, Delaware, accidentally received 500 chicks instead of her usual 50. Rather than send them back, she raised them for meat and sold the survivors at 62 cents a pound. The next year she scaled up to 1,000 birds. Word of her profits spread quickly across the Delmarva Peninsula, the coastal region spanning Delaware, Maryland, and Virginia.
The numbers tell the story of how fast things moved. Broiler production on the peninsula jumped from 50,000 birds in 1925 to 7 million by 1934. By 1941, farmers there were producing 48 million broilers a year. This was the birth of the commercial poultry industry, and it established the basic template for factory farming: raise large numbers of animals in confinement, optimize for fast growth, and sell at volume.
Mechanization and the 1930s
The early 1900s had already set the stage. Advances in refrigeration and transportation created demand that traditional farming couldn’t meet. The scale of animal production grew rapidly in the first decades of the century, but a key turning point came in the 1930s with the first mechanical slaughtering of animals. This made it possible to process far more animals than hand methods ever could, removing one of the major bottlenecks in the supply chain. Once you could kill and process thousands of animals a day, the incentive to raise thousands of animals at a time followed naturally.
Antibiotics and the Post-War Boom
The 1940s introduced a discovery that would reshape livestock production: antibiotics could make animals grow faster. Researchers found that animals fed feed containing antibiotic residues gained weight more quickly, even at low doses. The effect worked by altering the bacterial populations in animals’ guts, improving how efficiently they converted feed into body mass.
This was transformative. Farmers could now pack more animals into tighter spaces because antibiotics reduced the disease outbreaks that would otherwise devastate crowded herds and flocks. Animals reached slaughter weight sooner, on less feed. The economics of confinement farming suddenly made sense at a scale that hadn’t been possible before. Routine antibiotic use in livestock feed became standard practice across the industry and remained so for decades.
The Green Revolution and Feedlots in the 1950s
The mid-century Green Revolution, which dramatically increased global grain production, provided the cheap feed that intensive animal farming needed to expand. With surplus corn and soybeans available at low prices, it became more economical to confine cattle in feedlots and bring the grain to them rather than let them graze on pasture.
The commercial cattle feedlot emerged in the 1950s as a direct result. Surplus feed grains combined with consumer demand for grain-finished beef, which has more marbling and a fattier taste than grass-fed beef. The modern feedlot industry expanded rapidly. Cattle would spend their final months packed into open-air pens, eating grain-based diets designed to add weight as fast as possible. This model replaced the older system where cattle spent their entire lives on rangeland, and it remains the dominant method of beef production in the U.S. today. Even now, 75% of cattle spend at least 45 days a year in concentrated feeding operations.
Environmental Regulations Catch Up in the 1970s
By the early 1970s, factory farms had grown large enough to create serious pollution problems. Animal waste from massive operations was contaminating rivers, lakes, and groundwater. The federal government responded with the 1972 Clean Water Act, which specifically defined feedlots as “point sources” of pollution, placing them in the same regulatory category as meat processing plants and fertilizer manufacturers.
The EPA established effluent guidelines for feedlots in 1974, requiring operations to control manure-contaminated wastewater and prevent it from reaching surface water. By 1976, the agency had created formal definitions for “concentrated animal feeding operations,” or CAFOs, the regulatory term for what most people call factory farms. These definitions set specific size thresholds: a large CAFO for cattle, for example, means 1,000 or more animals. For chickens raised for meat, the threshold is 125,000 birds. For hogs over 55 pounds, it’s 2,500.
The creation of these regulations was an acknowledgment that animal farming had become an industrial operation with industrial-scale environmental consequences. But the regulations focused narrowly on water pollution and did little to slow the industry’s growth.
Consolidation From the 1980s Onward
The decades after the 1970s saw relentless consolidation. Smaller farms couldn’t compete with the efficiency of large operations, and federal farm policy did little to protect them. The number of farms shrank while the number of animals on each surviving farm grew. Dairy farming followed the same trajectory as poultry and beef. Automated milking parlors became available in the 1990s, allowing complete automation of the milking process and making it feasible for a single operation to milk thousands of cows with minimal labor.
The result is the system that exists today. According to estimates from the Sentience Institute using USDA census data, 99% of livestock in the U.S. were factory-farmed as of 2022. The figures are especially stark for poultry: more than 99% of chickens and turkeys are raised in confinement. More than 98% of hens and pigs live on factory farms. Globally, the picture is similar though slightly less concentrated. An estimated 74% of land livestock worldwide are factory-farmed. When farmed fish are included, that number rises to 94%.
A Century-Long Timeline
Factory farming didn’t arrive all at once. It assembled itself piece by piece over about 100 years:
- 1923: Commercial broiler chicken production begins on the Delmarva Peninsula
- 1930s: Mechanical slaughter makes large-scale processing possible
- 1940s: Antibiotics discovered as growth promoters, enabling higher animal density
- 1950s: Commercial cattle feedlots emerge, fueled by cheap surplus grain
- 1972–1976: Federal regulations first define and attempt to regulate concentrated animal feeding operations
- 1990s: Automated milking and continued consolidation push dairy farming toward the factory model
- 2020s: An estimated 99% of U.S. livestock now raised in factory farm conditions
Each stage built on the last. Refrigeration and transport created demand. Mechanized slaughter removed processing limits. Antibiotics made confinement viable. Cheap grain made it profitable. And once the economics tipped in favor of scale, smaller operations steadily disappeared. What began as a regional poultry experiment in coastal Delaware became, within a single century, the dominant way the world produces meat, eggs, and dairy.