As farming has industrialized, the interdependent agricultural cycle of plants and animals has been disconnected. Animals raised for meat and other products are given feed formulated to speed their growth to market weight, rather than the grasses, insects, seeds and other foods they would naturally eat.

Advocates of industrial farming argue that today’s feed is specially formulated to supply all essential nutrients; however, such grain-based diets can produce serious and sometimes fatal digestive problems in ruminants (including cows, goats and sheep), whose stomachs are evolved to naturally digest grass, not grain. For hogs and poultry in confinement, both the formulation of feed and the frequency of feeding are designed to accelerate growth at unhealthy rates.

The Political Economy of Feed

Current industrial farming practices rely heavily on grain, particularly corn and soybeans. Conventional animal feed is composed largely of these grains, because together they provide the carbohydrates and protein necessary for bringing animals quickly to market weight, and because they are cheaper than other feed options as a result of government subsidies. According to a 2006 study by the Tufts University Global Development and Environment Institute (the last time these numbers were crunched), the market prices of chicken and hog feed, made mostly of corn and soybeans, were 21 and 26 percent below the cost of production of these grains. Feed accounts for 60 percent of broiler chicken production costs; therefore, the price difference in the 2006 study reveals that total costs of broiler production were 13 percent lower than they would have been had the grains been priced at their full costs. This “discount” saved the broiler chicken industry an average of $1.25 billion annually between 1997 and 2005. The savings to large hog operations was $1 billion in the same period. For industrial dairies, beef and egg producers, plus hogs and broilers, the combined total savings over the nine years was nearly $35 billion. Also note that pricing grain below cost is bad for grain farmers, even when some of the difference is made up by subsidies or crop insurance.

Independent livestock farmers trying to compete with industrial production, supplementing their animals’ grazing with hay, food scraps, minerals or other feedstock not made of corn and soybeans, are at an economic disadvantage, because these stocks are not subsidized in the same way. In fact, according to the Tufts study, the cost advantages to industrial producers would be significantly reduced, if not eliminated, were they required to pay full cost for feed.

Confinement feed is also subsidized in many states by a tax exemption on the sale of livestock feed. This exemption benefits any farmer buying feed, but provides an increased benefit to large confinement operations, which buy all of their feed. Conversely, individual farmers who pasture their livestock and who therefore do not purchase much feed do not receive much benefit. State sales tax exemptions are also common for other staples of CAFOs, including livestock bedding, poultry litter and pollution control (meaning in practice the construction and management of manure lagoons). Such incentives to large operations also result in losses of state revenue.

Health Implications of Feed Types for Animals and People

Feeding animals foods they cannot naturally digest has consequences for both the animals and the people consuming their meat and other products.

Cows are ruminants, which means that they can digest the cellulose in grass in their multi-chambered digestive tracts. 1 Beef cattle are raised on grass for the first part of their lives, but are then moved to a feedlot where they are fed rations composed of 70 to 90 percent grain. From then until they reach market weight, several months later, cattle consume about six pounds of feed for every pound of weight they gain. Eating grain can cause severe health problems in cattle, including liver abscesses, bloat and sudden death syndrome. 2 Studies have shown that the incidence of liver abscesses in cattle decreases significantly when more roughage, such as grass or hay, is added to their diets. 3

6 pounds

of feed required per pound a cow gains in weight

Grain-fed cattle also have high acidity in their digestive tracts, which can lead to a proliferation of E. coli O157:H7. This bacterial strain has evolved to survive in high-acid environments and therefore can withstand one of the human body’s main defenses against pathogens: the acidic stomach. If in the slaughter and butchering process cattle carcasses come into contact with other carcasses contaminated with feces containing O157:H7, this pathogen can enter our food supply. 4

In many states, food waste can be fed to hogs, but it must be properly heat-treated to eliminate risk of pathogens. Diseases that hogs could contract and spread arising from improperly treated food waste include foot and mouth disease, African swine fever, Salmonella and toxoplasmosis. 5 Animal feed often contains antibiotics and other drugs, which can have serious consequences. For years, arsenic was a common additive to poultry feed, but the US Food and Drug Administration withdrew approval for use of the last arsenic additives to animal feed in 2015. Antibiotics, however, continue to be a significant public health concern. From 2009 to 2014, domestic sales and distribution of antibiotics approved for use in food-producing animals increased by 22 percent. 6 Ninety-seven percent of these drugs were purchased over the counter and are commonly administered through feed or water (making precise dosing impossible 7), which can speed the evolution of antibiotic-resistant bacteria. According to the World Health Organization, antibiotic-resistance in many areas of the world already exceeds 50 percent in several major bacteria groups, including E. coli, K. pneumonia, and S. aureus. 8 While the US Food and Drug Administration (FDA) passed a rule in 2017 that banned antibiotic use for growth promotion and require a veterinarian’s prescription, the use of the drugs for disease prevention is still allowed. 9

Metals like copper and zinc are given to pigs and chickens in feed (in excess of what their bodies need) to promote growth and prevent disease (the latter especially in “antibiotic free” CAFOs); these metals can be excreted out as animal waste. 10 Other metals present in animal waste can include cadmium, lead, mercury and arsenic. 11 The metals can accumulate in soil when animal waste is sprayed on farm fields and can lead to metal contamination of both soil and water. 12 13 In humans, copper toxicity can cause gastrointestinal and liver disorders and other health problems. 14 Copper can also cause environmental problems, including negative effects to soil microbial activity and plant growth and can be toxic to fish and aquatic life in waterways. 15 Zinc pollution can cause fish kills and damage to algae, crustaceans and salmon. 16

The Pasture-Fed Alternative

Raising animals on pasture takes advantage of their ability to feed themselves, provides food natural to their digestion and fertilizes a farm’s soil in the process. The “pasture-raised” process varies across different species; however, all most animals, depending on what species and what climate they live in, may require supplements to their foraged diet, especially in winter. These supplemental feed mixes are sometimes based on corn and soybeans, just as they are for animals in confinement; the difference is that the feed is just one part of the diet, rather than the total, and for USDA certified Organic animal products, must come from feed grown with out pesticides or synthetic fertilizers.

Cattle can be fed entirely on grass (including hay and silage in the winter); many pasture-based farmers also provide minerals that may be lacking in the pasture and, as discussed above, some feed-supplemental grains, such as corn, soybeans, barley or oats. In such cases, cattle are not considered 100 percent grass-fed. Hogs can be raised efficiently on food waste, including vegetable scraps, spent brewery grain, excess milk or eggs, as well as from foraging in harvested fields or wooded areas. 17 If the diet does not include enough protein, it can be supplemented with a protein-rich feed mix. Chickens raised on pasture eat insects and seeds, though various feed mixes make up the bulk of their diet, especially in winter. 18

For human health, there is a growing body of evidence that products from pastured animals are healthier than those from animals raised in confinement. Beef from grass-fed animals has lower levels of unhealthy fats and cholesterol and higher levels of vitamins, antioxidants and omega-3 fatty acids, which are better for cardiovascular health. 19 Meat from animals raised entirely on grass also has nearly twice the levels of conjugated linoleic acid (CLA), an amino acid linked to decreased cancer risk. 20 Eggs from pastured hens have been shown to have twice as much vitamin E and total omega-3 fatty acids as eggs from commercially raised hens. 21

What You Can Do

  • Look for beef and dairy products labeled “pasture raised” and “100 percent grassfed” or bearing a comparable designation of no supplemental grain feeding. The label “certified Organic” on pork, chicken and eggs indicates, among other practices, that all of the feed eaten by the animals was grown organically. Products bearing the Animal Welfare Approved label have met rigorous certification standards, including for feed.
  • Learn more about food labels from our Food Label Guide.
  • If you purchase animal products at a farmers’ market, you can always ask about their feeding practices.

Hide References

  1. Orr, Adam, PhD. (n.d.). How Cows Eat Grass. US Food and Drug Administration, Animal Health Literacy. Retrieved from
  2. Vasconcelos, J.T. (2008). “ASAS Centennial Paper: Contributions in the Journal of Animal Science to understanding cattle metabolic and digestive disorders.” Journal of Animal Science. Vol. 86 No. 7, p. 1711-1721. Retrieved from
  3. Reinhardt, C.D. and M.E. Hubbert (2015). “Review: Control of liver abscesses in feedlot cattle: A review.” The Professional Animal Scientist. 31:101–108. Retrieved from,PAS.v32n2.p101-108.2015.pdf.
  4. Segelken, H. Roger (1998). “Simple Change in Cattle Diet Could Cut E. Coli Infection.” Cornell Chronicle. Retrieved from
  5. Myer, R. O. and Westendorf, M. L. (2004/2015). “Feeding food wastes to swine.” University of Florida Institute of Food and Agricultural Sciences Extension. Retrieved from
  6. Food and Drug Administration (December 2015). 2014 Summary Report on Antimicrobials Sold or Distributed for Use in Food-Producing Animals. Department of Health and Human Services. Retrieved from  
  7. Pew Charitable Trusts (May 6, 2016). FDA Policies on Antibiotic Use in Food Animals. Retrieved from  
  8. World Health Organization (April 2014). Antimicrobial resistance: global report on surveillance 2014. Retrieved from  
  9. McKinna, M. (2017). After years of debate, the FDA finally curtails antibiotic use in livestock. Newsweek. Retrieved from:
  10. Jay, J., DeRouchey, J., Tokach, M., Goodband, R., Nelssen, J., Renter, D., Dritz, S. Fact Sheet: High dietary levels of copper and zinc for young pigs. American Association of Swine Veterinarians. Retrieved from:  
  11. Dai, S., Jones, B., Lee, K., Li, W., Post, L., Herrman, T. (2016). Heavy Metal Contamination of Animal Feed in Texas. Journal of Regulatory Science. Retrieved from:
  12. Jackson, B., Bertsch P., Cabrera M., Camberato J., Seaman J., Wood C. (2003) Trace element speciation in poultry litter. Journal of Environmental Quality. Retreived from:  
  13. Rodriguez-Eugenio, N. et al. (2018) Soil Pollution: A Hidden Reality. Food and Agriculture Organization. Retrieved from 
  14. National Research Council. (2000). Copper in Drinking Water. Washington, DC: The National Academies Press. Retrieved from:
  15. Irwin, R. (1997). Environmental Contaminants Encyclopedia: Copper Entry. National Parks Service. Retrieved from:
  16. Irwin, R. (1997). Environmental Contaminants Encyclopedia: Zinc Entry. National Parks Service. Retrieved from:
  17. Gegner, Lance (2001). “Organic Matters: Considerations in Organic Hog Production.” National Sustainable Agriculture Information Service. Retrieved from
  18. Mattocks, J. (2002). “Pasture-raised Poultry Nutrition.” Heifer International / USDA Sustainable Agriculture Research and Education, Southern Region. Retrieved from
  19. Clancy, K. (2006). Greener Pastures: How Grass-fed Beef and Milk Contribute to Healthy Eating. Union of Concerned Scientists. Retrieved from
  20. Daley, Cynthia, et al (2010). “A review of fatty acid profiles and antioxidant content in grass-fed and grain-fed beef.” Nutrition Journal. 9:10. Retrieved from  
  21. Karsten, H.D., et al (2010). “Vitamins A, E and fatty acid composition of the eggs of caged hens and pastured hens.” Renewable Agriculture and Food Systems 25(01). Retrieved from