3. Animal Feeding Operations

Animal feeding operations (AFOs) are lots or facilities in which confined animals are fed, raised, and maintained.¹⁹⁴ Unlike farms that allow livestock to graze or be integrated into crop production, AFOs are focused on one task: maximizing the production of meat, dairy, or eggs.

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certain size threshold or, in some circumstances, if they discharge waste into surface waters.¹⁹⁵

There are roughly 450,000 AFOs¹⁹⁶ in the United States, including 20,000 CAFOs.¹⁹⁷ CAFOs alone hold the majority of the country’s foodproducing animals.¹⁹⁸ While AFOs are credited with lowering consumer costs for animal products, they have considerable externalities. They can harm animal welfare, increase antibiotic resistance due to the routine use of antibiotics,¹⁹⁹ emit air and water pollution,²⁰⁰ depress property values,²⁰¹ hurt small-scale farms and businesses,²⁰² and diminish quality of life in rural communities.²⁰³

There are AFO systems for production of all types of meat—beef, pork, and poultry—as well as production of eggs and dairy products. While the details vary, in general, swine and dairy AFOs often rely on liquid manure systems, poultry and egg AFOs produce a dry litter, and cattle feedlots leave the animal waste on the open ground. In liquid systems, workers wash the manure from the animal pens to a storage lagoon, usually uncovered, where it is eventually pumped out and spread onto fields.

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AFO manure management systems produce much more methane than pasture-based livestock operations. When manure is left as a solid (as naturally happens on grazing lands and pasturelands), it typically decomposes aerobically and produces little to no methane.

AFOs produce an enormous amount of waste and emit tremendous amounts of greenhouse gases. Iowa’s 4,000 hog AFOs generated more than 68 billion pounds of manure in 2019, 68 times the amount of human excreta produced by the state’s residents, according to a conservative estimate.²⁰⁶ Meanwhile, Wisconsin’s 8,600 dairy farms are estimated to have generated almost 28 million tons of manure in 2018²⁰⁷—more than 50 times the amount of human excreta produced within the state.²⁰⁸ And since human waste must be treated before being released into the environment, reducing both the threat of pathogens²⁰⁹ and volume of organic material discharged, the relative impact from CAFO waste is even more stark—a CAFO with 250 dairy cows produces more organic waste every day than does a city the size of Albany.²¹⁰ As a result of their reliance on anaerobic

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storage practices, dairy and hog operations are responsible for almost 90% of methane emissions from manure management.²¹¹ When comparing net greenhouse gas emissions from AFO systems, however, it is important to take into account other factors as well, including enteric emissions and the greater length of time that may be needed for animals to reach market weight in pasture-based systems.

This section evaluates four different strategies for reducing emissions from AFOs. The first strategy—transitioning to integrated crop-livestock systems—offers the most significant co-benefits, although its impact on greenhouse gas emissions will vary considerably by animal type and breed, the local environment, and other factors. The second strategy focuses on the benefits of eliminating concentrated liquid manure, which, as discussed above, is the dominant source of emissions from manure management.

Reincorporate animals into croplands. The most effective way to reduce emissions from AFOs would be to replace them with well-managed integrated crop-livestock systems. Traditionally, most farms incorporated animals into cropping systems by allowing them to forage on plant residues after harvest, but early agricultural scientists and extension agents discouraged this practice, perceiving it as archaic and inefficient. As late as 1974, 19% of farms in the United States used a crop-grazing rotation, accounting for 52% of cropland.²¹² By 2012, only 7% of farms used livestock in their rotations on less than 2% of all cropland.²¹³ As scientists have begun to understand the ecology of agriculture better, however, they have started to encourage it as an environmentally friendly way to intensify agricultural

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production.²¹⁴ Some even argue that crop-livestock farms are economically and environmentally optimal, creating an efficient nutrient cycle between plants and animals.²¹⁵

Mixed crop-livestock systems increase inputs of plant litter and manure into soil along with the impacts of living plant roots and livestock, which can increase soil health and carbon sequestration. They can substantially reduce methane emissions from manure management because manure in integrated systems is typically left to decompose aerobically.²¹⁶ As noted above, however, both animal growth rates and enteric emissions must be taken into account when comparing net emissions from different systems of animal agriculture.

In addition to their climate benefits, properly managed crop-livestock systems naturally control pest and weed populations²¹⁷ and can improve soil structure, animal health, water quality, and biodiversity.²¹⁸

Eliminate concentrated liquid manure.

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Industry advocates claim that biogas reduces greenhouse gas emissions, but these assertions rely on unfounded assumptions and overly optimistic projections, while ignoring methane leakage and more effective forms of manure management. Digesters reduce methane emissions when compared to unregulated liquid manure management systems, but liquid manure management systems have the highest per-head methane emission rates among all methods of manure management.²²⁰ Instead of comparing biogas to the most carbon-intensive system—and ignoring other methods, as anaerobic digestion proponents often do—we should compare it to other systems currently in use. When we do this, we find that is not only the most expensive method for reducing manure emissions, but it is also among the least effective.

Dairy and swine industrial facilities produce 90% of manure management emissions because they typically rely on liquid management systems, where manure is washed from animal pens to storage lagoons. This produces emissions rates as much as 90 times higher than those found in grazing-based and other dry manure systems.²²¹ Anaerobic digestion can reduce the scale of these emissions, but digesters still release a considerable amount of methane. Large-scale, well-managed digesters can achieve leakage rates around 3% in optimal conditions²²²—much less than some studies have found²²³—but still enough to make digestion an inferior method of reducing emissions.²²⁴ In addition, the natural gas supply chain has a leakage rate of 2.3%,²²⁵ if not higher,²²⁶ adding to the amount of methane emitted by digesters.

While anaerobic digestion may reduce emissions relative to conventional liquid manure management, it is less beneficial to the climate than dry management and pastured-based alternatives—and, in contrast to those alternatives—it reinforces highly polluting practices. As discussed infra in Chapter VI.D, liquid manure systems also decrease soil, air, and water quality in rural

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communities, while lowering property values, regardless of whether anaerobic digestion is used.

Improve spreading of concentrated liquid manure. The Clean Water Act requires that the manure be spread at “agronomic rates”—that is in quantities that the plants need and can use.²²⁷ However, that provision is often ignored, with the result that manure can pollute nearby waters and release greenhouse gases.²²⁸ There is some evidence that specific practices relating to manure spreading can also affect emissions and soil carbon sequestration levels. Spreading on frozen or saturated soils, for example, tends to lead to water pollution and higher nitrous oxide emissions because the manure is more likely to enter waterways instead of being incorporated into the soil.²²⁹

Develop methane inhibitors and vaccines. A number of feed additives have been demonstrated to decrease methane emissions from livestock in shortterm experiments.²³⁰ When studied over the long term, however, these effects disappear or decrease significantly as the microflora in livestock’s rumen adapt to the new diet.²³¹ Nonetheless, scientists are studying novel approaches that they hope will remain effective throughout a ruminant’s life-span. One study documented a 30% decrease in enteric methane emissions over 12 weeks with the addition of 3-nitrooxypropanol, a chemical compound that blocks an enzyme critical to methane formation.²³² Another promising study found that red seawood supplementation reduced enteric emissions from cattle by 80% over 5 months.²³³

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Other researchers have developed vaccines designed to reduce methane emissions.

Finally, research indicates that eliminating antibiotic use in livestock may reduce the prevalence of methane-producing archaea. As a result, eliminating the nontherapeutic use of antibiotics in animals could have an effect on emissions similar to that of methane inhibitors and vaccines. Animals in confined production facilities routinely receive antibiotics to increase their growth rates and to prevent disease.²³⁶ This alters the microbiota of confined animals, affecting their health and physiology,²³⁷ and may increase the amount of methane-producing microflora. For example, a 2016 study showed that tetracycline, a common antibiotic used in livestock production, nearly doubled methane emissions from cow dung.²³⁸ Future research will be necessary to test additional classes of antibiotics and confirm that the effect will hold for enteric emissions.²³⁹ Nonetheless, these initial results are promising.

Eliminating nontherapeutic antibiotic use in livestock would reduce the development of new resistance genes and the transmission of antibiotic resistance from animals to humans.²⁴⁰ While new chemical inhibitors and vaccines may prove to be an effective and important pathway for reducing

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greenhouse gas emissions, they are unlikely to have significant social or environmental co-benefits. As with any feed additive or animal drug, their effects on animal welfare and human food safety should be rigorously assessed prior to marketing.