# Environmental impact of cattle

The production of cattle has a significant environmental impact, whether measured in terms of methane emissions, land use, consumption of water, discharge of pollutants, or eutrophication of waterways.
Estimated virtual water requirements for various foods (m$^3$ water/ton) :
| | Hoekstra & Hung (2003) | Chapagain & Hoekstra (2003) | Zimmer & Renault (2003) | Oki et al. (2003) | Average |
| Beef | | 15,977 | 13,500 | 20,700 | 16,730 |
| Pork | | 5,906 | 4,600 | 5,900 | 5,470 |
| Cheese | | 5,288 | | | 5,290 |
| Poultry | | 2,828 | 4,100 | 4,500 | 3,810 |
| Eggs | | 4,657 | 2,700 | 3,200 | 3,520 |
| Rice | 2,656 | | 1,400 | 3,600 | 2,550 |
| Soybeans | 2,300 | | 2,750 | 2,500 | 2,520 |
| Wheat | 1,150 | | 1,160 | 2,000 | 1,440 |
| Maize | 450 | | 710 | 1,900 | 1,020 |
| Milk | | 865 | 790 | 560 | 740 |
| Potatoes | 160 | | 105 | | 130 |
Significant numbers of dairy, as well as beef cattle, are confined in concentrated animal feeding operations (CAFOs), defined as "new and existing operations which stable or confine and feed or maintain for a total of 45 days or more in any 12-month period more than the number of animals specified" where "[c]rops, vegetation, forage growth, or post-harvest residues are not sustained in the normal growing season over any portion of the lot or facility." They may be designated as small, medium and large. Such designation of cattle CAFOs is according to cattle type (mature dairy cows, veal calves or other) and cattle numbers, but medium CAFOs are so designated only if they meet certain discharge criteria, and small CAFOs are designated only on a case-by-case basis.
A CAFO that discharges pollutants is required to obtain a permit, which requires a plan to manage nutrient runoff, manure, chemicals, contaminants, and other wastewater pursuant to the US Clean Water Act. The regulations involving CAFO permitting have been extensively litigated.
Commonly, CAFO wastewater and manure nutrients are applied to land at agronomic rates for use by forages or crops, and it is often assumed that various constituents of wastewater and manure, e.g. organic contaminants and pathogens, will be retained, inactivated or degraded on the land with application at such rates; however, additional evidence is needed to test reliability of such assumptions. Concerns raised by opponents of CAFOs have included risks of contaminated water due to feedlot runoff, soil erosion, human and animal exposure to toxic chemicals, development of antibiotic resistant bacteria and an increase in E. coli contamination. While research suggests some of these impacts can be mitigated by developing wastewater treatment systems and planting cover crops in larger setback zones, the Union of Concerned Scientists released a report in 2008 concluding that CAFOs are generally unsustainable and externalize costs.
Another concern is manure, which if not well-managed, can lead to adverse environmental consequences. However, manure also is a valuable source of nutrients and organic matter when used as a fertilizer. Manure was used as a fertilizer on about 6,400,000 hectares (15.8 million acres) of US cropland in 2006, with manure from cattle accounting for nearly 70% of manure applications to soybeans and about 80% or more of manure applications to corn, wheat, barley, oats and sorghum. Substitution of manure for synthetic fertilizers in crop production can be environmentally significant, as between 43 and 88 megajoules of fossil fuel energy would be used per kg of nitrogen in manufacture of synthetic nitrogenous fertilizers.
Grazing by cattle at low intensities can create a favourable environment for native herbs and forbs by mimicking the native grazers who they displaced; in many world regions, though, cattle are reducing biodiversity due to overgrazing. A survey of refuge managers on 123 National Wildlife Refuges in the US tallied 86 species of wildlife considered positively affected and 82 considered negatively affected by refuge cattle grazing or haying. Proper management of pastures, notably managed intensive rotational grazing and grazing at low intensities can lead to less use of fossil fuel energy, increased recapture of carbon dioxide, fewer ammonia emissions into the atmosphere, reduced soil erosion, better air quality, and less water pollution.

## Methane and nitrous oxide emissions

The Food and Agriculture Organization estimates that in 2015 around 7% of global greenhouse gas emissions (GHG) were due to cattle, but this is uncertain. Another estimate is 12% of global GHG. More recently Climate Trace estimates 4.5% directly from cattle in 2022. Reducing methane emissions quickly helps limit climate change.
Estimates by Climate TRACE :
| Billion tonnes CO2eq (% of total global emissions) | 2022 |
| Enteric fermentation cattle feedlot | 7.95 (1.76) |
| Enteric fermentation cattle pasture | 8.55 (1.90) |
| Manure left on pasture cattle | 2.91 (0.65) |
| Manure management cattle feedlot | 0.70 (0.16) |
| Total | 20.11 (4.47) |
Gut flora in cattle include methanogens that produce methane as a byproduct of enteric fermentation, which cattle belch out. Additional methane is produced by anaerobic fermentation of manure in manure lagoons and other manure storage structures. Manure can also release nitrous oxide. Over 20 years atmospheric methane has 81 times the global warming potential of the same amount of atmospheric carbon dioxide.
As conditions vary a lot the IPCC would like these taken into account when estimating methane emissions, in other words countries where cattle are significant should use Tier 3 methods in their national greenhouse gas inventories. Although well-managed perennial pastures sequester carbon in the soil, as of 2023 life cycle assessments are required to fully assess pastoral dairy farms in all environments.

### Ways to reduce methane emissions being considered

Methane belching from cattle might be reduced by intensification of farming, selective breeding, immunization against the many methanogens, rumen defaunation (killing the bacteria-killing protozoa), diet modification (e.g. seaweed fortification), decreased antibiotic use, and grazing management.
Agricultural subsidies for cattle and their feedstock could be stopped. A more controversial suggestion, advocated by George Monbiot in the documentary "Apocalypse Cow", is to stop farming cattle completely, however farmers often have political power so might be able to resist such a big change.