Environmental Implications of Modern Animal Agriculture: Save the Planet with your Fork

Lacey Gaechter, University of Colorado




This report is designed to provide readers with peer-reviewed scientific or governmental information regarding the environmental impacts of the United States’ animal agriculture industry. All the information is carefully cited so that readers may easily investigate sources. Several calculations were required in order to understand some industry trends, but the sources of the numbers used are readily available for confirmation. All general references to animal agriculture in this paper include the beef, dairy, pig, poultry, and sheep industries. The report excludes statistics on fish, fur, wool, insect, or any other type of animal farming not listed above. The goal of this paper is to provide substantiated and verifiable evidence that animal agriculture negatively affects global environmental quality.




Today America consumes more animal products per person than almost any other society in history. The scale of modern animal agriculture, along with specific industry practices has substantial impacts on human health, animal welfare, and the global environment. The following report specifically examines the environmental impacts associated with today’s animal operations.


The form that animal agriculture has taken in the last 50 years has greatly compounded environmental problems. Since that time, the size of the industry has increased dramatically, while the number of farmers in the industry has decreased. As Figure 1 clearly illustrates, animal agriculture has become increasingly consolidated in recent years. This trend toward concentration has compounded pollution problems associated with animal waste.


Because of the basic chemistry behind energy transfers, animal agriculture requires a great deal of plant matter to support it. In turn, the production of this excessive plant matter requires tremendous resources in the form of land, water, and energy. Furthermore, the enormous size and concentration of the animal industry has caused serious problems regarding pollution and waste disposal. The large scale consumption of animal products in the United States has a dramatic effect on natural systems.


Consolidation of animal agriculture industry

Farm Category

Time Period

% Growth in industry

% Decrease in number of producers













Fig. 1. This table shows that although the listed industries have increased in size,
the number of producers in each category has decreased substantially.
Information taken from Copeland 2002, p. 187.




According to the United States Department of Agriculture (USDA), over 66.9 million acres of harvested cropland is dedicated to growing fodder for the animals that people eventually use for food (1999, p. 39 and 41). This number equals roughly 22 percent of harvested cropland (16 percent of all cropland) in the United States. Furthermore, this acreage must be added to the 461 million acres occupied as pasture and grazing land in order to account for the total area dedicated to the production of meat, eggs, and dairy. In total, the industry occupies roughly 528 million acres, or 57 percent of all domestic agricultural land (USDA 1999 p. 21). It is important to note that if all Americans ate a purely vegetarian diet, at least 461 million acres of pastureland would become available for other purposes.




It is difficult to determine exactly how much water is used in the animal agriculture industry. A U.S. Geological Survey study estimated that domestic animal operations consumed nearly two billion gallons of water per day in 1990. This figure, however, only represents water used at animal-raising and slaughtering facilities. It does not account for water required to grow the crops used to feed the animals.


Crops raised for animal feed occupied roughly 11 million irrigated acres in 1997 according to the USDA Agricultural Census (see Fig. 2 in Appendix A). Irrigation consumes a particularly large amount of water per acre for several reasons. A great deal of water is often lost in association with irrigation through evaporation from open storage areas (e.g. reservoirs) and open transport canals and aqueducts. Furthermore, irrigation is generally needed in arid regions that almost inevitably experience particularly high evaporation rates (see Fig. 3 in Appendix A). The remaining 55 million acres dedicated to growing animal feed do not consume nearly as much water as do the irrigated lands. Even on non-irrigated farms, however, a tremendous amount of water is still lost to the atmosphere through the evapotranspiration that is necessary for crops to grow. Although exact numbers on water use in animal agriculture are not available, it is clear that the industry uses large amounts of this resource. Again, only a fraction of the water currently used would be needed to support a purely vegetarian population.




Governmental or scientific information on the amount of petroleum used in U.S. agriculture is not currently available. The 1997 USDA Census of Agriculture does, however, list the costs associated with the use of petroleum and chemicals on farms. The study sampled varying numbers of farms for their total expenditure on these products and compiled the data listed in the table below (see Fig. 4). The total average amount spent on petroleum products per farm based on these data was $14,199. The same census listed the total number of U.S. farms at 1,911,859, which means that national agricultural spending on petroleum products was approximately $27 billion in 1997 (p. 96). The study also lists agricultural spending on fertilizers and other chemicals. Data regarding these  goods found that the average farm spent $16,116 in 1997, making total industry spending on these products $31 billion (see Fig. 5).


Money spent on petroleum in 1997





# of Farms Surveyed

$1,000 spent

Ave. $ spent/ farm (rounded to whole $ amt.)





Diesel Fuel




Natural gas




LP gas, fuel oil, kerosene, motor oil, grease, etc.




Other Petroleum products




Ave. Total Spent




Fig. 4. This chart lists the expenditures of surveyed farms on various petroleum products
and then averages the money spent per farm. Information taken from USDA 1999, p. 98.



Money spent on fertilizers and agricultural chemicals in 1997





# of Farms  Surveyed


Ave. $ spent (rounded to the whole $ amt.)

Commercial Fertilizers




Agricultural Chemicals




Ave. Total Spent




Fig. 5. This table illustrates average spending per farm on various agricultural products.
Information taken from USDA 1999, p. 98.


Numbers on how much of this spending came from the animal agriculture industry are not readily available. Based on land-use, however, it is possible to make reasonable estimates through calculations. Petroleum products are probably used roughly equally in the crop industry and the animal industry. Both types of agriculture must transport their goods, and they both rely heavily on machinery to operate their businesses. As a result, it is probably fair to say that if animal agriculture uses a total of 57 percent of agricultural land in the United States, it also uses 57 percent of the petroleum products in the industry, or roughly $15 billion worth. Certainly, cropland requires a great deal more fertilizer and other agricultural chemicals than do animal farms. Considering this fact, the money spent on agricultural chemicals as part of the animal industry is probably close to 16 percent (percentage of cropland used to feed animals) of the total. This number is still an impressive $5 billion. Although these estimates are rough, they give some insight into the extent to which the production of animals for food contributes to the use of petroleum and other chemical products in the United States. In turn the use of these products leads to the destruction of land for their extraction, and the release of pollutants in their consumption.




The most commonly studied source of pollution from animal farms is not related to fossil fuels, but to organic matter, including manure, bedding, uneaten feed, and carcasses. In one study, Copeland estimates that animal agriculture in the United States produces 112 million tons of dry manure each year, making this the industry's most abundant waste product (2002, p. 187).


Amount of manure produced by various animals


Type of animal

Manure produced in lbs/yr/1,000 lb of animal mass



Broiler chickens


Layer hens


Breeding hens and turkeys


Dairy cows


Fig. 6. This table lists the amount of manure produced by each type of animal shown.
Information was not available for all animal used for food.
It is helpful to compare this data with Fig. 7 in Appendix A,
which lists the number of animals in each industry, although weights must be estimated.
Information taken from EPA 2002, p. 6-3 through 6-23.




Fertilizing Crops

The EPA reports that roughly 99 percent of dairy operations distribute their waste overland, in an attempt to fortify the soil. They also note, however, that 36-61 percent of small (200-700 milking cows) dairies have insufficient land to absorb the nutrients of their manure, while 14 percent have no land at all. Fifty-one to sixty-eight percent of large facilities (>700 milking cows) have insufficient land, and 22 percent have no land (EPA 2002, p. 4-83). This discrepancy is sometimes remedied by distributing manure on another farmer's land, but nutrients from animal waste often far exceed regional needs. In 1998 Carpenter et al found that "nutrient flows to aquatic ecosystems are directly related to animal stocking densities, and under high livestock densities, manure production exceeds the needs of crops to which the manure is applied" (p. 559). In this case, nutrients become pollutants and can be toxic to living systems.



Lagoons are the most common depository for waste throughout the animal industry. These basins catch organic matter and allow it to decompose aenerobically into harmless compounds. The reliability of lagoons, however, has come under serious question due to their frequent structural failures, and consequent spills (Copeland 2002). Mallin et al studied swine and poultry waste lagoon spills in North Carolina, and found in both cases that the spills caused harmful disturbances to water quality of the effected streams. The results showed changes to turbidity and dissolved oxygen, pollution levels of nitrogen (N) and phosphorous (P), dense phytoplankton blooms, and high fecal coliform concentrations. In a separate study conducted by Burkholder et al, a swine waste lagoon failure led to similar results, but in this case a fish kill of 4,000 individuals was also reported (Burkholder et al 1997). Copeland states that large-scale lagoon spills have occurred in almost every state in the U.S. (2002), and Mallin et al specifically note 30 reported spills from animal waste lagoons in 1995 and 1996 in North Carolina alone (1997).


Properly operating lagoons have also been studied for efficacy. In a 2002 Iowa study, Simpkins et al found that 50 percent of the earthen lagoon constraints in the study sample leaked at a rate greater than 1.6 mm/day, even under new state regulations. Furthermore, the researchers speculated that up to 5,000 unregulated lagoons existed in the state, and likely experienced far more substantial leaks. Whether functioning within required limits or not, animal waste lagoons often pose a serious threat to local environmental quality.


Efficacy of Controls

Many regulations are in place to curb the effects of pollution from animal farms, but inquiries into their efficacy have not been inspiring. Centner et al estimate that 80 percent of animal feeding operations in the United States are not permitted by the EPA, and therefore do not comply to its standards (2002).


Manure Contents and Effects on Ecosystems

The contents of animal manure is well documented, and the effects of these constituents on bodies of water is being thoroughly studied. The 2002 EPA report lists the "Key Pollutants in Animal Waste" as nitrogen (N), phosphorus (P), potassium (K), organic compounds, solids, pathogens, salts, trace elements, and volatile compounds (p. ES-7 – ES-8). These and other substances enter water bodies through leaks, infiltration through soil into groundwater, and directly through erosion and runoff and when animals have access to flowing water (EPA 2002). Agriculture is the number one cause of water pollution in the United States, and is responsible for roughly 70 percent of polluted waterways. Twenty percent of this 70 percent is said to originate from the animal production industry (Copeland 2002, p. 189). Furthermore, 16 percent of the pollution from crop raising comes from land used to grow fodder. In a smaller study, Nord et al judged that 66 percent of N and 78 percent of P output in one watershed originated from wasted animal feed and manure, when most of the farms in the study area split their land between growing cash crops and animal production (2003). Clearly, animal agriculture is a much larger polluter than is crop farming.


Once they have reached waterways, the pollutants in manure can cause a great deal of damage to aquatic and human life. A 2001 EPA report points to fish kills as the biggest problem associated with pollutants from manure (p. 1-5). Smith et al found that excessive amounts of P and N in fresh water causes excessive algal blooms, which adversely affect native populations by altering the chemical, thermal, and radiative aquatic environment. Accumulations of these nutrients in the ocean cause toxic phytoplankton blooms, which lead to fish kills (1999). Nitrogen can also become a global pollutant when released into the atmosphere, eventually settling back into distant water ways (Carpenter et al 1998; Aneja et al 1998).


Manure can be dangerous for people in a few forms. Organisms that are deadly to humans can make their way into the food supply through water contaminated with animal waste. Though direct contamination is not common, components of manure can also affect drinking water quality. These problems compound as practicality encourages animal operations to locate closer to heavily populated areas (EPA 2001). These facilities pose a serious threat to human health as well as to the health of local and global ecosystems.




The current world-wide growth in population and affluence is putting global resources under increasing pressure. Agriculture is a major consumer of land, water, and energy. Animal farming is responsible for roughly half of this resource exploitation and is a major source of pollution to natural systems. Although it is unreasonable to think that all Americans might become vegetarian, a simple reduction in the amount of animal products that this country consumes could mean enormous relief for non-renewable resources. This type of diet change has the capacity to decrease the United States' agricultural land, water, and petroleum needs by up to 50 percent.  A diet that includes fewer animal products will also greatly decrease the amount of pollution in waterways, increasing the health of these ecosystems. Decidedly, one of the most profound and positive impacts an American can have on the planet comes from a simple change in eating habits.

Works Cited


Aneja, V.P., Murray, G.C., Southerland, J. (1998). Atmospheric nitrogen compounds: Emissions, transport, transformation, deposition, and assessment. Environmental Management, 48 (4), 22-25.


Burkholder, J.M., Mallin, M.A., Glasgow, H.B., Jr., Larsen, L.M., McIver, M.R., Shank, G.C., Deamer-Melia, N., Briley, D.S., Springer, J., Touchette, B.W., Hannon, E.K. (1997). Impacts to coastal river and estuary from rupture of large swine waste holding lagoon. Journal of Environmental Quality, vol. 26, no. 6, 1451-1466.


Carpenter, S.R., Caraco, N.F., Correll, D.L., Howarth, R.W., Sharpley, A.N., Smith, V.H. (1998). Nonpoint pollution of surface waters with phosphorous and nitrogen. Ecological Applications, 8 (3), 559-568).


Centner, T.J., Mullen, J.D.(2002). Enforce existing animal feeding operations regulations to reduce pollutants. Water Resource Management, vol. 16, no. 2, 133-144.


Copeland, Claudia (2002). Animal production, feedlots, and manure problems in the US. Encyclopedia of Global Environmental Change, vol. 7, 187-190.


EPA (2001). Environmental and economic benefit analysis of final revision to the national pollutant discharge elimination system regulation and the effluent guidelines for concentrated animal feeding operations, 1-3 through 1-6.


EPA (2002). Environmental and economic benefit analysis of final revision to the national pollutant discharge elimination system regulation and the effluent guidelines for concentrated animal feeding operations, 1-1 through 6-26.


Mallin, M.A., Burkholder, J.M., McIver, M.R., Shank, G.C., Glasgow, H.B., Jr, Touchette, B.W., Springer, J. (1997). Comparative effects of poultry and swine waste lagoon spills on the quality of receiving streamwaters. Journal of Environmental Quality, vol. 26, no. 6, 1622-1637.


Nord, E.A., Lanyon, L.E. (2003). Managing material transfer and nutrient flow in an agricultural watershed. Journal of Environmental Quality, 32, 562-570.


Simpkins, W.W., Burkart, M.R., Helmke, M.F., Twedt, T.N., James, D.E., Jaquis, R.J., Cole, K.J. (2002). Potential impact of earthen waste storage structures on water resources in Iowa. Journal of the American Water Resources Association, vol. 38, no. 3, 759-772 .


United States Department of Agriculture, National Agricultural Statistics Service (1999). 1997 census of agriculture: United States summary and state data (AC97-A-51).


United States Geological Survey (1990). Estimated use of water in the United States in 1990: Livestock water use. Retrieved from http://water.usgs.gov/watuse/tables/lvtab.huc.html October 29, 2003.


United States Geological Survey (1999). Water science map gallery. Water science for schools. Retrieved from http://ga.water.usgs.gov/edu/tables/dlir.html Dec. 7, 2003.



Appendix A



Irrigated Acres By Crop Type


Type of crop

Irrigated Acres

Corn for silage or green chops


Sorghum for silage or green chops


Hay (all types)


Field seed and grass seed crops


Alfalfa seed




Fig. 2. This chart is simply available to illustrate the source of numbers cited in the report.

Information taken from USDA 1999, p. 40.





Fig. 3. This map clearly illustrates the correlation between arid regions and high levels of irrigation.

Figure taken from USGS Water science 1999. 





Total census of animals in agriculture in 1997





Type of animal

Number in millions


 Type of animal

Number in millions 






layer hens



cattle and calves










beef cows



























Milk Cows


















Total animals


Fig. 7. This census was taken from the USDA Agricultural Census. Some information was listed repetitively in the USDA report and is shown in the same way here to avoid error (p. 21-34).