Cattle feeding

Different cattle feeding production systems have separate advantages and disadvantages. Most cows have a diet that is composed of at least some forage (grass, legumes, or silage). In fact most beef cattle are raised on pasture from birth in the spring until autumn (7 to 9 months). Then for pasture-fed animals, grass is the forage that composes all or at least the great majority of their diet. Cattle fattened in feedlots are fed small amounts of hay or straw supplemented with grain, soy and other ingredients in order to increase the energy density of the diet. The debate is whether cattle should be raised on diets primarily composed of pasture (grass) or a concentrated diet of grain, soy, corn and other supplements. The issue is often complicated by the political interests and confusion between labels such as "free range", "organic", or "natural". Cattle raised on a primarily forage diet are termed grass-fed or pasture-raised; for example meat or milk may be called grass-fed beef or pasture-raised dairy. However, the term "pasture-raised" can lead to confusion with the term "free range", which does not describe exactly what the animals eat.

Cow eating grass

Typology of animal production systems

Grazing systems

Animals grazing in rangelands, pastures and grasslands and with little or no integration of crops involved. About 60% of the world's pasture land is covered by grazing systems.Grazing systems supply approximately 9 percent of the world's production of beef, according to Food and Agriculture Organization FAO statistics. ^[1]

Integrated livestock-crop farming systems

Animal productions are integrated with crop productions. Moreover, livestock such as cattle are primarily fed on pastures, crop residues and fallows. An integrated farming system consists of a range of resource-saving practices that aim to achieve acceptable profits and high and sustained production levels. Mixed farming systems are the largest category of livestock system in the world. ^[2]

Industrial production systems

Animals are fed in landless environments such as in stalls, pens and feedlots in very high stocking densities. Intensive or industrial factory farming of animals originated in the United States in the late 1930s. This has resulted in an integrated model of production, where large corporations control most aspects of animal husbandry in the food industry, processing of animals into food products, and sales to the consumer market.

Industrial productions systems differ from grazing systems and integrated livestock-crop farming systems by their inclusions of various substances such as veterinary drugs, growth hormones, feed additives or nutraceuticals to improve livestock production effectiveness.^[3]

Country specific

Canada

The majority of beef cattle in Ontario are finished on a corn (maize)-based diet, whereas Western Canadian beef is finished on a barley-based diet. This rule is not absolute, however, as producers in both regions will alter the mix of feed grains according to changes in feed prices. Research by the Ontario government claims that, while Alberta beef producers have organized a successful marketing campaign promoting Alberta's barley-fed beef, corn-fed and barley-fed beef have a similar cost, quality, and taste.^[4]

Beef safety and governmental regulation

The aim of the beef industry and the government regulatory system in Canada is to provide a safe and wholesome product to consumers. Regulations on veterinary drug use in food animals and drug-residue testing programs ensure that the product in the grocery store is free of residue from antibiotics or synthetic hormones used in livestock.

The Animal Nutrition Association of Canada has developed a comprehensive HACCP (Hazard Analysis Critical Control Points) system for animal feed production called FeedAssure. This mandatory HACCP Based Program includes a requirement for independent audits of feed mills including production processes and record keeping. The Canadian Cattlemen's Association has also developed a HACCP based on-farm food safety program.

A complete HACCP system is mandatory for all federally inspected establishments. These systems include prerequisite programs, which are general procedures or good manufacturing practices (GMPs) that enhance food safety for all meat production processes. HACCP plans build on this foundation and are designed to control potential hazards for specific production processes.^[5]

United States

According to the United States Department of Agriculture (USDA) there are 25,000,000 to 33,000,000 head of feed cattle moving through custom and commercial cattle feedyards annually. The semi-annual USDA "Cattle on Feed Report" is available for public viewing.

The feed cattle enterprise is an industry where millions of dollars move through these custom and private cattle feeding facilities every year. The business of feeding cattle is based on a commodity market mechanism. Both corn and cattle are bought and sold via commodity market prices. This makes for huge variations within the final outcome of profit and loss within the enterprise. However, the Chicago Mercantile Exchange (CME) provides producers with options or hedges for smoothing price volatility and risk. Additionally, forward contracts and pre-paying for feedstuffs counteracts the variation in both commodities.

Style of Feeding

There are many segments of the USA cattle business.

1. Seed stock, where producers breed for improved genetics
2. Cow/calf, where ranchers and farmers raise cows and calves for commercial production
3. Stocker/grower, where producers place light weight calves on pasture, wheat or corn stocks
4. Grow yards/back grounding facilities, where high forage diets are fed to light weight feeder calves weighing 350 pounds (160 kg) to 500 pounds (230 kg) to be fed to the weight of 750 pounds (340 kg) to 900 pounds (410 kg) pounds
5. Custom/Commercial Finishing yards, where cattle are fed to harvest at the weight of 1,000 pounds (450 kg) to 1,500 pounds (680 kg) pounds. Once the fed cattle are sold for harvest they are shipped for processing and distribution to the consumer.

Use of growth stimulants

Antibiotics are routinely added to grain feed as a growth stimulant. Livestock consume 70% of the antibiotics in the United States.^[6] This practice contributes to the rise of antibiotic-resistant bacteria, including MRSA.^[7] The most common form of antibiotics are called ionophores. Ionophores were originally developed as coccidiostats for poultry and prevent coccidiosis in cattle as well. Ionophores work by improving both feed efficiency and growth rate and lower methane production as one result. Ionophores have not been shown to create antibiotic-resistant MRSA.^[8]

Use of hormones

The use of growth hormones is controversial. The benefits of using growth hormones includes improved feed efficiency, carcass quality and rate of muscle development. It is argued that with the use of growth hormones more plentiful quality meats can be sold for affordable prices. Growth hormones are often not well looked upon due to the use of synthetic hormones and also fears about the consumption of these hormones from the meat products. Due to the fact that synthetic hormones are unnatural, there are concerns about how it could affect the bodily functions of consumers. The long term effects of the consumption of synthetic hormones have not been thoroughly examined.^{[citation needed]} Using hormones in cattle costs $1.50 and adds between 40 and 50 pounds to the weight of a steer at slaughter, for a return of at least $25.^[9]

American regulators permit hormone use on the grounds that no risk to human health has been proven, even though measurable hormone residues do turn up in the meat we eat. These contribute to the buildup of estrogenic compounds in the environment, which some scientists believe may explain falling sperm counts and premature maturation in girls.^{[citation needed]} Recent studies have also found elevated levels of synthetic growth hormones in feedlot wastes; these persistent chemicals eventually wind up in the waterways downstream of feedlots, where scientists have found fish exhibiting abnormal sex characteristics.^[9]

Safety level of hormone use in cattle

In Canada, all veterinary drugs used in food production processes are required to pass stringent tests and regulations set by the Veterinary Drugs Directorate (VDD) and are enforced by the Food and Drug Act of Health Canada. The CFIA monitors all food products in Canada by sampling and testing by veterinarians and inspectors working on behalf of the provincial and federal governments. They monitor the food supply to condemn and destroy any product that is unacceptable. In the rare case where the CFIA have found a residue, it has been substantially below the Maximum Residue Limit (MRL) to make acceptable for safe consumption. The MRL is the maximum amount of a drug residue that may remain in a food product at the time of human consumption. MRLs are safety measures based on Accepted Daily Intakes (ADIs).^[10] The ADI level is determined from toxicology studies to be the highest amount of a substance that can be consumed daily throughout a lifespan without causing adverse effects.^[11] Beef hormone residues are MRLs that have been established by the Joint Expert Committee on Food Additives of the United Nations.^[10] Although there is growing concern that hormone residues in meat and milk might be harmful to human and animal health, the quantities of hormones found in a serving of meat are far below the level considered to be a risk to the development of cancer. Besides, the World Health Organization stated that the hormone levels are indistinguishable between the implanted and nonimplanted animals.^[11]

There are three natural hormones (estradiol or estrogen, progesterone and testosterone) and their synthetic alternatives (zeranol, melengestrol acetate, and trenbolone acetate) have been approved by the VDD for use in Canadian beef production.^[10]

Estrogen, progesterone and testosterone are naturally present in beef cattle regardless of whether or not they have been treated with hormones. Despite the fact these hormones are also present in human, the contribution of estrogen, progesterone and testosterone from beef is minuscule compared to the quantities produced naturally in the body. By comparison, an adult male will produce 136,000 ng of estrogen on a given day; whereas the estrogen levels present in a 6-ounce serving of beef from a treated animal is only approximately 3.8 ng.^[10] In another word, a human being will produce almost 36,000 times the amount of estrogen in one day that would be present in a piece of beef produced with the growth hormones treated.^[10] Thus, the quantities of hormones found in a serving of meat are far below the level considered to be a risk to the development of cancer. Current scientific evidence does not support that pubescent maturation is caused by the hormonal substance use in animals.^[11]

Artificial hormone debate

Bovine somatotropin or bovine growth hormone is a naturally produced protein in cattle. Recombinant bovine somatotropin (rBST) or recombinant bovine growth hormone (rBGH) is an artificial growth hormone produced using microbes with modified (recombinant) DNA, the same way human insulin is made for diabetics. It is approved in the United States since 1993; however, its use has been controversial since farmers have started using it.^{[citation needed]}

USDA label

The United States Department of Agriculture's Agricultural Marketing Service (AMS) released a revised proposal for a grass fed meat label claim for its process-verified labeling program in May 2006. ^[12] The Union of Concerned Scientists, which in general supports the labeling proposal, claims that the current revision, which contains the clause "consumption of ... grain in the immature stage is acceptable", allows for "feed harvesting or stockpiling methods that might include significant amounts of grain" because the term "immature" is not clearly defined. ^[13]

On October 15, 2007 the USDA established a standard definition for the "grass fed" claim which requires continuous access to pasture and prevents animals from being fed grain or grain-based products.^[14]

Rest of World

Trading

Beef production tends to be concentrated, with the top six producers—the U.S., the European Union, Brazil, Australia, Argentina, and Russia—accounting for about 60 percent of global production. Significant shifts among producers have occurred over time. Cattle production worldwide is differentiated by animal genetics and feeding methods, resulting in differing quality types. Cattle are basically residual claimants to crop or land resources. Those countries with excess or low-value land tend to grass-feed their cattle herds, while those countries with excess feed grains, such as the U.S. and Canada, finish cattle with a grain ration. Grain-fed cattle have more internal fat (i.e., marbling) which results in a more tender meat than forage-fed cattle of a similar age. In some Asian countries such as Japan, which is not a grain surplus country, tastes and preferences have encouraged feeding grain to cattle, but at a high cost since the grain must be imported.^{[15] [16]}

Grass fed

Cut fodder being transported to feed cattle in Tanzania

Grass-fed cattle at a Walcha, NSW sale.

Stud Murray Grey cows receiving supplementary feeding during a drought.

Grass fed or pasture-fed cattle, grass and other forage compose most all or at least the great majority of the grass fed diet. The debate is whether cattle should be raised on diets primarily composed of pasture (grass) or a concentrated diet of grain, soy and other supplements. The issue is often complicated by the political interests and confusion between labels such as "free range," "organic" or "natural." Cattle raised on a primarily forage diet are termed grass-fed or pasture-raised; meat or milk may be called grass-fed beef or pasture-raised dairy. However, the term "pasture-raised" can lead to confusion with the term "free range" which does not describe exactly what the animals eat. Another term is "grass-finished."

Corn fed

Cattle called "corn-fed," "grain-fed" or "corn-finished" are typically fattened on corn, soy and other types of feed for several months before slaughter. As a high-starch, high-energy food, corn decreases the time to fatten cattle and increases yield from dairy cattle. Some corn-feed cattle are fattened in concentrated animal feeding operations.

In the United States, most grass-fed cattle are raised for beef production. Dairy cattle may be supplemented with grain to increase the efficiency of production and reduce the area needed to support the energy requirements of the herd.

A growing number of health and environmental proponents in the United States such as the Union of Concerned Scientists advocate raising cattle on pasture and other forage. Complete adoption of farming practices like grass-fed beef production systems would increase the amount of land needed to raise beef but reduce land used to grow soy and corn to feed them.^[17]

Health and nutrition

Fats

Most grass-fed cattle are leaner than feedlot beef, lacking marbling, which lowers the fat content and caloric level of the meat. Meat from grass-fed cattle also have higher levels of conjugated linoleic acid (CLA) and the omega-3 fatty acids ALA, EPA, and DHA.^[18]

Flax (or linseed) (Linum usitatissimum) is one of the most biologically available botanical sources of omega-3 fatty acid which is high in protein and ALA (alpha-linolenic acid). Recently, research has been conducted involving the use of ground flax seeds as a fat supplement in cattle rations. Being high in protein and fats, it can easily replace other energy dense foods such as corn. It is believed that the inclusion of omega-3 fatty acids in the diets of beef producing cattle will bring an increase in health to the animals and to the quality of carcass upon slaughter.^[19] Some studies have found that feeding flax seeds may increase the omega-3 content and improve marbling in the carcass of the animal at slaughter while others have found no differences. Flax seeds suppress inflammatory effects from bovine respiratory disease (BRD) often affecting stressed cattle due to production practices such as transport and processing. BRD can lead to lung tissue damage and impair the performance of the cattle leading to a low final body mass at slaughter or premature death. Another effect of feeding flax in cattle ration is an observed increase in the daily dry matter intake.^[20] This was observed in feeding a total dietary content of omega-3 fatty acids of under 10% of total feed. Although the direct beneficial effects of feeding omega-3 fatty acids remain uncertain, the preventative effect from feeding omega-3s to stressed cattle have shown great promise. Although flax feeds are greatly more expensive compared to other feeds, the economical benefits from having a generally healthier herd of cattle outweighs the cost^{[citation needed]}

Antibiotics

Antibiotics are commonly used in the food production system as a way to control the growth of potentially harmful bacteria. Potential benefits from the use of antibiotics include the prevention of diseases, increase in food and water uptake, and increase the digestive effectiveness of the animal. There are concerns however about residues of the antibiotics getting into the milk or meat of cattle. In Canada, The Canadian Food Inspection Agency (CFIA) enforces standards which protects consumers by ensuring that foods produced will not contain antibiotics at a level which will cause harm to consumers.^[11] In America, the government requires a withdraw period for any animal treated with antibiotics before it can be slaughtered, to allow residue to exit the animal.^[21]

However, less intense population density is sometimes cited ^[22] as a reason for decreased antibiotic usage in grass-fed animals. However, bovine respiratory disease, the most common cause for antibiotic therapy has risk factors common in both forms of production (feedlot and pasture finished).^[23]

In dairy herds, grazed cattle typically have a reduced need for antibiotics relative to grain-fed cattle, simply because the grazed herds are less productive.^[22] A high-energy feedlot diet greatly increases milk output, measured in pounds or kilograms of milk per head per day, but it also increases animal physiological stress,^[22] which in turn causes a higher incidence of mastitis and other infectious disease, more frequently requiring antibiotic therapy.^{[citation needed]}

There are two distinctions between the clinical and nonclinical use of antibiotics in cows. Clinical use of antibiotics refers to the treatment of cows due to sickness. However, corn-fed cattle draw attention to the nonclinical use of antibiotics. Antibiotics are used to promote growth and treat sick cattle, yet the cattle would not get sick if they were not fed a corn-based diet that subjects them to diseases caused by the malfunctioning of their rumen.</ref>^{[24][citation needed]}

Safety Level of Antibiotic Use in Cattle

In Canada, the veterinary drug regulation, consisting of two federal government agencies, namely Health Canada(HC) and the CFIA, are responsible for implementing the Food and Drugs Act, and enforcing those standards and policies, respectively.^[11]

Testing for Drug Residues samples include three(3) proper methods: monitoring, surveillance, and compliance. These procedures are given to Swab Test On Premises (STOP) to detect antibiotic residues in kidney tissues.^[11]

Antibiotics and the Cattle Industry

Antibiotics are used in the cattle industry for therapeutic purposes where they are used in the treatment of infections, prophylactically for disease prevention, and as growth promoters. The latter means that there is an increased efficiency of feed use, where growth is stimulated with less feed. Ultimately, this results in reduced costs for cattle producers, and for consumers.^[11]

Antibiotic Resistance

Antibiotic resistance is a naturally-occurring phenomenon throughout the entire world due to the overuse and/or inappropriate use of the substance. However, its usage is supported primarily because of its effectiveness in the treatment and prevention of diseases, as well as its role as growth promoters. Antibiotic is also present in antibacterial cleaning products, and in disinfection products used in farm and veterinary practices.^[11] Therefore, antibiotic resistance could be on the rise.

Diseases

E. coli

Escherichia coli, although considered to be part of the normal gut flora for many mammals (including humans), has many strains. Strain E. coli 0157:H7 is associated with human illness (and sometimes death) as a foodborne illness. A study by Cornell University ^[25] has determined that grass-fed animals have as much as 80% less of this strain of E. coli in their guts than their grain-fed counterparts, though this reduction can be achieved by switching an animal to grass only a few days prior to slaughter. Also, the amount of E. coli they do have is much less likely to survive our first-line defense against infection: stomach acid. This is because feeding grain to cattle makes their normally pH-neutral digestive tract abnormally acidic; over time, the pathogenic E. coli becomes acid-resistant.^[26] If humans ingest this acid-resistant E. coli via grain-feed beef, a large number of them may survive past the stomach, causing an infection.^[27] A study by the USDA Meat and Animal Research Center in Lincoln Nebraska (2000) has confirmed the Cornell research.^{[28][dubious – discuss]}

Mad cow disease

Main article: Bovine spongiform encephalopathy

Meat and bone meal can be a risk factor for bovine spongiform encephalopathy (BSE), when healthy animals consume tainted tissues from infected animals. People concerned about Creutzfeld-Jacob disease (CJD), which is also a spongiform encephalopathy, may favor grass-fed cattle for this reason. In the United States, this risk is relatively low as feeding of protein sources from any ruminant to another ruminant has been banned since 1997.^[29] The problem becomes more complicated as other feedstuffs containing animal by-products are still allowed to be fed to other non-ruminants (chickens, cats, dogs, horses, pigs, etc.). Therefore, at a feed mill mixing feed for pigs, for instance, there is still the possibility of cross-contamination of feed going to cattle.^{[citation needed]} Since only a tiny amount of the contaminating prion begins the cascading brain disease, any amount of mixed feed could cause many animals to become infected.^{[citation needed]} This was the only traceable link among the cattle with BSE in Canada that led to the recent US embargo of Canadian beef.^{[citation needed]} No cases of BSE have been reported so far in Australia. This is largely due to Australia's strict quarantine and bio-security rules that prohibit beef imports from countries known to be infected with BSE.

However, according to a report filed in the Australian, on February 25, 2010, those rules were suddenly relaxed and the process to submit beef products from known BSE infected countries was allowed (pending an application process).^[30] But less than a week later, Tony Burke, the Australian Minister For Agriculture, Fisheries and Forestry swiftly overturned the decision and placed a 'two year stop' on all fresh and chilled beef products destined for Australia from BSE known countries of origin, thereby relaxing fears held by Australians that contaminated US beef would find its way onto Australian supermarket shelves after a long absence.^[31][32]

Soybean meal is cheap and plentiful in the United States. As a result, the use of animal byproduct feeds was never common, as it was in Europe. However, U.S. regulations only partially prohibit the use of animal byproducts in feed. In 1997, regulations prohibited the feeding of mammalian byproducts to ruminants such as cows and goats. However, the byproducts of ruminants can still be legally fed to pets or other livestock such as pigs and poultry such as chickens. In addition, it is legal for ruminants to be fed byproducts from some of these animals.^[33] A proposal^{[weasel words]} to end the use of cow blood, restaurant scraps, and poultry litter (fecal matter, feathers) in January 2004 has yet to be implemented,^[34] despite the efforts of some advocates of such a policy^[who?], who cite the fact that cows are herbivores, and that blood and fecal matter could potentially carry BSE.

In February 2001, the USGAO reported that the FDA, which is responsible for regulating feed, had not adequately policed the various bans.^[35] Compliance with the regulations was shown to be extremely poor before the discovery of the Washington cow, but industry representatives report that compliance is now 100%. Even so, critics^[who?] call the partial prohibitions insufficient. Indeed, US meat producer Creekstone Farms alleges that the USDA is preventing BSE testing from being conducted.^[36]

Campylobacter

Campylobacter, a bacterium that can cause another foodborne illness resulting in nausea, vomiting, fever, abdominal pain, headache and muscle pain was found by Australian researchers to be carried by 58% of cattle raised in feed lots versus only 2% of pasture raised and finished cattle.^[37]

BLV

Bovine Leukemia virus is insect-borne and found in 20% of US cows, and 60% of US herds. Studies in Sweden and the Soviet Union have linked BLV outbreaks and increases in human leukemia. BLV and HTLV-1 share a common gene, HTLV-1 is the first human retrovirus ever shown to cause cancer.

Environmental concerns

In arid climates such as the Southwestern United States, livestock grazing has severely degraded riparian areas, the wetland environment adjacent to rivers or streams. People^[who?] have long recognized that riparian zones and rivers are the lifeblood of the western landscape,^{[citation needed]} being more productive and home to more plants and animals than any other type of habitat^{[citation needed]}. Scientists refer to riparian zones as hotspots of biodiversity, a characterization that is particularly apparent in arid and semiarid environments^[38] (like Nevada, where over 80% of the 300 represented terrestrial wildlife species are "directly dependent on riparian habitat"), where such zones may be the only tree-dominated ecosystems in the landscape^{[citation needed]}. The presence of water, increased productivity, favorable microclimate, and periodic flood events combine to create a disproportionately higher biological diversity than that of the surrounding uplands.^[39]

"According to the Arizona state park department, over 90% of the original riparian zones of Arizona and New Mexico are gone". A 1988 report of the GAO was equally grim, estimating that 90% of the 5,300 miles of riparian habitat managed by the BLM in Colorado was in unsatisfactory condition, as was 80% of Idaho's riparian zones, concluding that "poorly managed livestock grazing is the major cause of degraded riparian habitat on federal rangelands."^[40]

Taste

The cow's diet affects the flavor of the resultant meat and milk. A 2003 Colorado State University study^[41] found that 80% of consumers in the Denver-Colorado area preferred the taste of United States corn-fed beef to Australian grass-fed beef, and negligible difference in taste preference compared to Canadian barley-fed beef.

Grass-fed beef is not standardized. Most is leaner than conventional feedlot beef, but some is equally marbled due to carefully managed grazing, excellent pastures, and improved genetics. Another technique for producing well-marbled grass-fed cattle is to keep the animals on pasture for two years or more. Most pasture-based ranchers dry-age the beef for 7–21 days, enhancing the flavor and tenderness of the meat.^{[citation needed]}

See also

• Free range
• Fodder
• Hay

References

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2. ^ Livestock & the environment: Finding a balance, Chapter 3: Mixed farming systems & the environment. Available online at: http://www.fao.org/docrep/X5303E/x5303e09.htm#chapter%203:%20mixed%20farming%20systems%20&%20the%20environment. Retrieved on 2009/12/4
3. ^ Silbergeld,E.K.,Graham,J.,and Price, L.B. (2008)Industrial Food Animal Production, Antimicrobial Resistance, and Human Health. Retrieved on Nov. 30, 2009, Available online at: http://arjournals.annualreviews.org/doi/pdf/10.1146/annurev.publhealth.29.020907.090904?cookieSet=1
4. ^ "Virtual Beef Newsletter - Corn or Barley for feeding Steers". Omafra.gov.on.ca. 2004-08-20. http://www.omafra.gov.on.ca/english/livestock/beef/news/vbn0804a3.htm. Retrieved 2009-11-08. 
5. ^ Canadian Beef. (2009). The Canadian Beef Industry. Retrieved on Nov. 30,2009, Available online at:http://www.canadianbeef.info/ca/en/rt/resources/default.aspx
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7. ^ Our Decrepit Food Factories. New York Times Pollan December 16, 2007
8. ^ Prince, S (2003) "Ionophores" Texas A&M Student Research Summary
9. ^ ^{a b} Pollan, Michael. (2002). Power steer. Retrieved from http://www.nytimes.com/2002/03/31/magazine/power-steer.html?pagewanted=7
10. ^ ^{a b c d e} Canadian Animal Health Institute (2003), Hormones: A Safe, Effective Production Tool for the Canadian Beef Industry. Retrieved on 2009 Oct. 30 Available online at: http://www.cahi-icsa.ca/pdf/Beef-Hormones-Factsheet.pdf
11. ^ ^{a b c d e f g h} Canadian Cattlemen’s Association and Beef Information Centre (2003), Understanding Use of Antibiotic and Hormonal Substances in Beef Cattle. Nutrition Perspective. Retrieved on 2009 Oct. 29 Available online at: http://www.afac.ab.ca/current/bichormones.pdf
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18. ^ http://www.ucsusa.org/assets/documents/food_and_environment/greener-pastures.pdf, p. 58
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23. ^ The medicine and epidemiology of bovine respiratory disease in feedlots. Australian veterinary journal Cusack 2003 vol:81 iss:8 pg:480-487 [3]
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40. ^ George Wuerthner, "The Price is Wrong", Sierra, September/October 1990
41. ^ Wendy Umberger, Dawn Thilmany and Amanda Ziehl, Department of Agricultural & Resource Economics, Colorado State University. 2003. "Consumer Tastes & Preferences: What Research Indicates". http://dare.agsci.colostate.edu/aft/curriculum/3.1_cons_prefs.ppt