Pigs crammed in a CAFO warehouse

Animal Feed

With the rapid rise of the industrial food animal production system, an increasing number of food animals once raised on pastures are now raised in feedlots. Feedlot-raised animals are kept indoors for the majority of the year, and they are given feed formulated to speed their growth to market weight and supply them with essential nutrients, while minimizing costs to operators. Concerns have arisen about the content of these feeds, however, as grain-based diets can produce serious and sometimes fatal digestive tract problems in food animals such as cows, goats, and sheep whose stomachs are best suited to digesting high-cellulose containing plants like grass.   1  In addition, recent studies have shown that chemical additives in feed may accumulate in animal tissues, potentially exposing consumers to unwanted chemicals such as veterinary drug residues and heavy metals.   2   3  It is important to consider how livestock feed affects animal health, and by extension the health of people who consume these animal products.

Corn and Soy

Current industrial farming practices rely heavily on grain. Under current US agriculture policy, the government provides substantial subsidies to farmers who produce grains, particularly corn and soybeans.   4  Livestock producers often use corn and soy as a base for their animal feed because these protein-rich grains help bring animals to market weight faster, and because they are cheaper than other feed options as a result of government subsidies. It has been estimated that the operating costs of factory farms  would be 7-10% higher without these subsidies.   6  As a result, a large percentage of grains grown in the US are used in animal feed, with 47% of soy and 60% of corn produced in the US being consumed by livestock.   6  

Although cheap feed grains mean lower meat and dairy prices for consumers, meat from grass fed animals is often lower in saturated fat than meat from grain fed animals. The FDA has reported that lowering the percentage of calories consumed from saturated fats may reduce the risk of heart disease.   7  While there is still more research to be done to examine the potential health benefits of consuming grass fed beef, initial findings indicate that other nutrients found in grass fed beef may be beneficial to the health of the consumer.

In order to meet the high demand for grain from industrial food animal operations, large corn and soy monocultures   have replaced many smaller farms, which rely on the heavy use of pesticides. Pesticides have been shown to “bioaccumulate” (or build-up) in the fatty tissues of animals, potentially exposing consumers to these chemicals via consumption of food animals that have consumed grains treated with these chemicals, even when care is taken to eliminate contamination during processing.   9  Exposure to pesticide has been shown to negatively affect reproductive, nervous and immune system functions, as well as increase the risk of developing cancer.   9

Dairy Cows and Beef Cattle
Cows are natural ruminants, which means that they are able to digest the cellulose in grass because of their multi-chambered digestive tracts.   10  Because ruminants' digestive systems are not designed for grain, cattle raised on grain can develop severe health problems, including liver abscesses, bloat, and sudden death syndrome.   11   12  Studies have shown that the incidence of liver abscesses in cattle decreases significantly as more roughage, such as grass or hay, is added to their diets.   13     14

Because the rumen of grain-fed cows is acidic, while that of grass-fed cows   is neutral due to different chemical processes, cows who are fed corn or soy based diets may be colonized with E.Coli strain O157:H7, a strain of e.coli   that has developed to withstand the acidic stomachs of cows raised on grain.   17  Consequently, this strain can withstand one of the human body’s main defenses against pathogens, the high acidity of the stomach,   18 increasing the risk of serious infection in people who consume meat contaminated with acidity-resistant strains.   19   20

Raising cattle on pasture not only makes sense for their digestive health, but also because it is an efficient use of natural resources, turning something we can’t eat – grass – into something we can – meat and dairy products. Pasture-based cattle operations also decrease soil erosion and improve soil fertility and water quality by maintaining grasslands which protect soils from water and wind erosion.   21   Unlike pasture raised animals, grain fed cattle are often raised on grass early in their lives, then moved to a feedlot where they are fed rations composed of 70 to 90 percent grain. From then until they reach market weight, anywhere from 90 to 300 days later, cattle consume about 6 pounds of feed for every one pound of weight gain.   22

According to the USDA’s agriculture census, since the late 1950s there has been a 24-fold decrease in the number of hog farms in the US and a 24-fold increase in the average number of hogs on each farm.   23   24 On industrial hog farms, these large herds are kept in crowded quarters, increasing the probability of agression between animals and making the spread of diseases easier because of close contact between hogs. To remedy these problems, many hogs have their tails cut off, a procedure known as “docking”, to reduce tail-biting,   25 and they are treated with antibiotics  to try to prevent the spread of disease between hogs.   27

In many states, processed food waste can be fed to pigs, but if this waste is not properly treated pigs that consume it may develop diseases such as hog cholera, Foot and Mouth Disease, African swine fever, and swine vesicular disease.   28 Hogs fed contaminated food wastes can also spread Salmonella, Campylobacter,Trichinella, and Toxoplasma, pathogens often responsible for foodborne illnesses, to other livestock and humans.   28  

In contrast, pastured pork production involves raising hogs outside on grass, legumes, standing crops, and other ground covers. Unlike ruminants, hogs require more nutrients than what pasture alone can provide, but a variety of crops like turnips, kale and fodder beets are excellent food sources, and letting hogs graze in harvested fields is an effective way to clear out the remnants while supplementing their diet. This diet, combined with good management practices, makes hogs some of the easiest animals to raise on pasture.   29   Hogs naturally want to root and dig during feeding, so allowing these behaviors in the pasture reduces aggression and agitation among members of the herd, improving the overall health of the animals. Hogs are also naturally competitive feeders, so allowing them to eat in the larger pasture area reduces injury to pigs due to competition in the confined quarters of the feedlot, also reducing the chance of infection or illness stemming from these injuries.   29

Industrial poultry farms raise chickens on feeds that have been formulated to maximize chicken growth and weight gain. However, these feed formulations often include medically important pharmaceutical drugs whose overuse by the poultry industry represents a threat to human health. Farms often use low doses of antibiotics to get their chickens to market weight faster, and low dose antibiotic use in food animals has been linked to the development of antibiotic resistant bacterial strains.   30 People infected with these strains have an increased risk of complications or death because these bacteria may have developed resistance to one or more of the limited number of antibiotic classes used on humans.   31

On industrial poultry farms, a range of antibiotics and additives is often added to poultry feed and water.   1 In 2011, the pharmaceutical company Pfizer temporarily suspended use of the poultry drug Roxarsone after FDA reports showing that the arsenical compounds in the drug may break down into inorganic arsenic, a toxin that can produce skin lesions, respiratory irritation, and several types of cancer in exposed persons,   32 and may leach into local water supplies or remain in chicken tissue after slaughter.   33   34 The effects of chronic low arsenic exposure are not well known, but studies have indicated that even low level exposure may contribute to endocrine and cognitive deficits.   35   36 Although Roxarsone use has been suspended, there are several other arsenical drugs in use that have the possibility of exposing consumers to toxic forms of arsenic.

A way to raise chickens without the health stresses of confinement is to pasture them. Although chickens can’t be raised entirely on grass, a natural chicken diet can include corn, oats, soybeans and dried alfalfa.   37 Many small farmers raise chickens on pasture using mobile structures that provide both shelter and feed to supplement foods like worms, grass and insects found on pastures.   38

The Results  
The overreliance on grain-based animal feeds in industrial food animal production has negative consequences for animal health, the environment, and even human health. Considering the natural eating habits of livestock animals when formulating animal feeds would be beneficial to both animals and consumers, and will result in healthier herds and flocks, less reliance on antibiotics to control disease, as well as a lower chance of introducing certain pathogens into society via contaminated meat.



    1. U.S. Department of Agriculture. (2010). Pastured poultry in Alabama. Natural Resources Conservation Service.
    2. Mattocks, J. (2002). Pasture-raised poultry nutrition. Colorado State University Cooperative Extension.
    3. Barber, R., Edwards, M., Gong, G., Menon, C., & O’Bryant, S. (2011). Long-term low-level arsenic exposure Is associated with poorer neuropsychological functioning: A Project FRONTIER study. International Journal of Environmental Research and Public Health, 8(3), 861-874.
    4. Fu, J. et al. (2010). Low-level arsenic impairs glucose-stimulated insulin secretion in pancreatic beta cells: Involvement of cellular adaptive response to oxidative stress. Environmental Health Perspectives, 118(6).
    5. Tennessee Department of Health. Arsenic fact sheet.
    6. U.S. Food and Drug Administration. (2011). Questions and answers regarding 3-Nitro (Roxarsone).
    7. Bean Freeman, L. E., Cantor, K. P., & Lubin, J. H. (2007). Inorganic arsenic in drinking water: An evolving public health concern. Journal of the National Cancer Institute.
    8. Burroughs, T., Knobler, S., Lemon, S., & Najafi, M. The resistance phenomenon in microbes and infectious disease vectors: Implications for human health and strategies for containment. Board on Global Health.
    9. Emanuele, P. (2010). Antibiotic resistance. American Association of Occupational Health Nurses Journal, 58(9).
    10. Gegner, L. (2001). Organic matters: Considerations in organic hog production. National Sustainable Agriculture Information Service.
    11. Myer, R. O., & Westendorf, M. L. Feeding food wastes to swine. University of Florida IFAS Extension.
    12. Bilkei, G., & Docic, M. (2003). Differences in antibiotic resistance in Escherichia coli, isolated from East-European swine herds with or without prophylactic use of antibiotics. Journal of Veterinary Medicine, 50(1), 27-30.
    13. Antibiotics
    14. Schroder-Petersen, D. L., & Simonsen, H. B. (2002). Tail biting in pigs. The Veterinary Journal, 162(3), 196-210.
    15. U.S. Department of Agriculture. Census of agriculture 1992 – 2007.
    16. U.S. Department of Agriculture. U.S. census of agricultural historical archive.
    17. USDA Economic Research Service. (2012). Cattle: Background.
    18. Clancy, K. (2006). Greener Pastures: How grass-fed beef and milk contribute to healthy eating. Union of Concerned Scientists.
    19. Alexander, T. W. et al. (2008). Effect of subtherapeutic administration of antibiotics on the prevalence of antibiotic-resistant Escherichia coli bacteria in feedlot cattle. Applied and Environmental Microbiology, 74(14), 4405-4416.
    20. De Vos, O., Diepeningen, A., Franz, E., & van Bruggen, A. (2005). Effects of cattle feeding regimen and soil management type on the fate of Escherichia coli O157:H7 and Salmonella enterica Serovar Typhimurium in manure, manure-amended soil, and lettuce. Applied and Environmental Microbiology, 71(10), 6165-6174.
    21. Jacob, M. E. et al. (2008). Feeding supplemental dried distiller’s grains increases faecal shedding of Escherichia coli O157 in experimentally inoculated calves. Zoonoses Public Health, 55(3), 125-132.
    22. Steele, M. A. et al. Bovine rumen epithelium undergoes rapid structural adaptations during grain-induced subacute ruminal acidosis.  American Journal of Physiology, 300 (6).
    23. E. coli
    24. Grassfed
    25. Chengappa, M. M., & Nagaraja, T. G. (1998). Liver abscesses in feedlot cattle: A review.  Journal of Animal Science, 76, 287-298.
    26. Uwituze, S. et al. (2009). Evaluation of dried distillers grains and roughage source in steam-flaked corn finishing diets. Journal of Animal Science, 88 (1), 258-274.
    27. Robinson, J. (2004). Pasture perfect. Vashon, WA: Vashon Island Press.
    28. Visser, D. P. Ruminant digestion. Department of Agriculture: Livestock Improvement Schemes.
    29. Fort Lewis College. Ruminant digestive system.
    30. Kelling, K., Lawrence, R., McKenzie, S., Rhubart-Berg, P., & Walker, P. (2005). Public health implications of meat production and consumption. Public Health Nutrition, 8 (4), 348-356.
    31. Monoculture
    32. U.S. Food and Drug Administration. (2009). Health claim notification for saturated fat, cholesterol, and trans fat, and reduced risk of heart disease.
    33. Institute for Agriculture and Trade Policy. (2006). Below-cost feed crops: An indirect subsidy for industrial animal factories.
    34. Factory Farm (Industrial Farm / Industrial Agriculture)
    35. Reidl, B. M. (2007). How farm subsidies harm taxpayers, consumers, and farmers, too.
    36. Horoszewicz, E., Niedziolka, R., & Pieniak-Lendzion, K. (2009). A study on bioaccumulation of selected metals in meat and internal organs of intensively fed kid goats.   Journal of Elementology, 14 (3), 501-507.
    37. James, C. A., Nesheim, M. C., & Yaktine, A. L. (2008). Nutrient and contaminant tradeoffs: Exchanging meat, poultry, or seafood for dietary protein. Nutrition Reviews, 66 (3), 113-122. Retrieved from
    38. Union of Concerned Scientists. (2006). They eat what? The reality of feed at animal factories.