Concentrated animal feeding operations, commonly called CAFOs, damage the environment in several overlapping ways: they generate massive volumes of greenhouse gases, contaminate waterways with nutrient-rich waste, spread antibiotic-resistant bacteria into surrounding ecosystems, and degrade air quality for nearby communities. These aren’t hypothetical risks. They’re well-documented consequences of concentrating thousands of animals in a single facility and managing the waste that comes with them.
What Counts as a CAFO
A CAFO is a livestock operation where animals are confined and fed in place rather than grazing on pasture, and it meets specific size thresholds set by the EPA. Large CAFOs house at least 1,000 cattle, 2,500 hogs, or 125,000 chickens, though medium and small designations also exist based on animal count and whether the facility discharges waste into waterways. Under the Clean Water Act, CAFOs are classified as point sources of pollution, meaning they’re subject to federal discharge permits. In practice, enforcement varies widely, and many operations fall through regulatory gaps.
Greenhouse Gas Emissions
Agriculture as a whole accounts for about 10.5 percent of all U.S. greenhouse gas emissions, totaling roughly 664 million metric tons of carbon dioxide equivalent in 2022. CAFOs contribute a disproportionate share of that total through two potent gases: methane and nitrous oxide.
Methane comes primarily from two sources on these operations. The first is enteric fermentation, which is the digestive process in cattle and other ruminants that produces methane as a byproduct. The second is manure management. When animal waste sits in the large, open-air lagoons that CAFOs rely on, bacteria break it down in oxygen-free conditions, releasing methane steadily into the atmosphere. Methane traps roughly 80 times more heat than carbon dioxide over a 20-year period, so even relatively small volumes have an outsized warming effect.
Nitrous oxide, the other major contributor, comes from how nitrogen in manure and fertilizer cycles through soil and water. The EPA estimated that nitrous oxide made up the single largest category of direct agricultural emissions in 2022 at 309 million metric tons of carbon dioxide equivalent. Nitrogen fertilizer application and manure management are the primary agricultural practices driving those numbers, and CAFOs are central to both: the waste they produce is often spread on nearby cropland as fertilizer, completing the cycle.
Water Contamination From Manure
A single large hog operation can produce as much raw waste as a small city, but unlike human sewage, that waste isn’t treated at a processing plant. Instead, most CAFOs collect manure in open lagoons or pits, then spray it onto surrounding fields. When the system works as intended, the soil absorbs the nutrients. When it doesn’t, the consequences for nearby waterways are severe.
Lagoon spills and runoff introduce enormous concentrations of ammonium, phosphorus, suspended solids, and fecal bacteria into rivers and streams. Research published in Environmental Health Perspectives documented that after CAFO waste spills, water conditions deteriorated for roughly 30 kilometers downstream from the point of entry. Dissolved oxygen dropped to near zero, ammonia levels spiked, and fecal coliform bacteria saturated the water column. Those conditions killed freshwater fish across every species present, from minnows and gar to largemouth bass, as well as estuarine species like striped bass and flounder farther downstream.
The spills also triggered blooms of toxic algae, which compound the damage by producing their own toxins and consuming even more oxygen as they decompose. But it’s not just the catastrophic spills that matter. Chronic, lower-level runoff from routine waste application on fields creates a slow, steady nutrient load that degrades water quality over years. Excess nitrogen and phosphorus from CAFO waste are major contributors to dead zones in coastal waters, where algal blooms strip oxygen from the water and make it uninhabitable for marine life.
Antibiotic Resistance in the Environment
Most animals in CAFOs receive antibiotics routinely, not just to treat illness but to promote faster growth and prevent disease in crowded conditions. A significant portion of those antibiotics pass through the animals unmetabolized and end up concentrated in manure lagoons. This creates ideal breeding grounds for bacteria that develop resistance to common drugs.
A U.S. Geological Survey study examining livestock lagoons across different operation types found antibiotic resistance genes for tetracycline and sulfonamide antibiotics present across the board. Swine lagoons showed the highest levels of sulfonamide resistance genes, which corresponded to the highest total antibiotic concentrations in those facilities. Critically, sulfonamide resistance genes proved more persistent than tetracycline resistance genes, meaning they survived longer in the environment and had more opportunity to spread.
These resistance genes don’t stay in the lagoon. They move into soil when waste is applied to fields, leach into groundwater, and travel downstream in runoff. Bacteria carrying resistance genes can also transfer those genes to other bacterial species through a process called horizontal gene transfer. The practical result is that antibiotic-resistant bacteria spread well beyond the boundaries of the farm itself, potentially reducing the effectiveness of common antibiotics in human medicine.
Air Quality and Nearby Communities
CAFOs release a mix of airborne pollutants that affect people living within several miles of the facility. Ammonia, hydrogen sulfide, and particulate matter are the main concerns. Ammonia volatilizes from manure lagoons and barns in large quantities, contributing to the formation of fine particulate matter that can travel long distances and aggravate respiratory conditions. Hydrogen sulfide, the gas responsible for the characteristic rotten-egg smell near these operations, causes headaches, nausea, and respiratory irritation at the concentrations commonly found downwind of large facilities.
These air quality impacts fall disproportionately on rural communities, often lower-income ones, that lack the political leverage to push back against facility siting decisions. Property values decline near CAFOs, and residents frequently report being unable to open windows, spend time outdoors, or hang laundry without it absorbing the odor. The health effects go beyond nuisance. Studies have linked proximity to large livestock operations with higher rates of asthma, respiratory infections, and impaired lung function in children.
Soil Degradation and Nutrient Overload
When manure is applied to fields at rates that match what crops can absorb, it functions as fertilizer. The problem is that CAFOs produce far more waste than surrounding land can use. Repeated overapplication saturates the soil with nitrogen and phosphorus, eventually exceeding the soil’s capacity to bind and process these nutrients. At that point, excess phosphorus accumulates in topsoil and washes into waterways with every rain, while excess nitrogen converts to nitrate and migrates downward into groundwater.
Elevated nitrate in drinking water wells is a well-known problem in regions with dense CAFO activity. Nitrate contamination is particularly dangerous for infants, in whom it can interfere with the blood’s ability to carry oxygen. For the soil itself, chronic overloading with CAFO waste can alter microbial communities, increase salt content, and introduce heavy metals like copper and zinc that are commonly added to animal feed. Over time, this degrades the soil’s long-term productivity, turning a theoretically renewable resource into one that requires increasing intervention to remain farmable.
Scale Makes the Difference
Livestock farming has always produced waste, emissions, and some degree of environmental impact. What makes CAFOs different is concentration. Traditional farms spread animals across enough land to absorb their waste naturally. A CAFO concentrates thousands of animals on a small footprint, generating waste volumes that overwhelm local ecosystems. The lagoon-and-sprayfield system most operations rely on was designed as a low-cost solution, not an environmentally sound one, and the gap between what these facilities produce and what the surrounding land and water can handle is the core of the problem.