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Animal agriculture in the United States utilizes antimicrobials for both subtherapeutic and therapeutic purposes. The majority of current use is subtheraputic, with antimicrobials provided in daily feed and

13 _{Key, Nigel and Stacy Sneeringer, “Climate Change Policy and the Adoption of Methane Digesters on}

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water sources at dosage levels below those used for therapeutic applications. This is done to increase growth rates, improve feed efficiency, and in some cases improve reproductive performance.

Pressure has emerged, however, both nationally and internationally, to reduce the use of subtherapeutic antimicrobials in animal agriculture. These initiatives began mostly in Europe – specifically in Sweden, Denmark, the United Kingdom, and finally the EU as a whole. The rationale most aggressively pushed is that sustained use of antimicrobials in animal production could lead to resistant organisms that might render antibiotics less effective for treatment of human disease.

Sweden was the first to implement a ban; in 1986, it banned the use of antimicrobials as growth

promoters. An analysis found that slaughter hogs, eggs, and specialized turkey and beef production exhibited no negative long-term effects associated with the ban.14 _{Broiler chicken and piglet production,}

however, did experience significant short-term impacts.

In piglet producing units, increased disease rates required an increase of therapeutic antibiotics. Post- weaning mortality rates during the first year post-ban increased by 1.5%, and the time to reach 55 pounds was increased by 5 to 6 days.15 _{Adjustments were then made to feed and herd management. In addition,}

zinc-oxide was used to prevent and cure diarrhea. “By September 1998 approximately 85% of piglets reached the age of delivery to fattening units without having been given either antibiotics or zinc-oxide.”16

In broiler production, necrotic enteritis surfaced as a major problem after the ban, and required virtually all chickens to be prescribed virginiamycin in 1987 to prevent the disease. A shift was later made to instead treat outbreaks by giving a two-day treatment of phenoxy methyl penicillin in drinking water to affected flocks. Adjustments were also made to reduce the protein content in chicken feed and increase fiber and coarse grains, and add enyzmes. Combined, the measures reduced antibiotic usage from two tons of virginiamycin in 1987 to 100 Kg of phenoxy methyl penicillin in 1988, and to a “negligible level” thereafter.17

Denmark was the second European country to adopt antimicrobial legislation. Denmark has progressively

tightened the rules regarding the use of antibiotics in food animals, both through bans on subtherapeutic usage, as well as regulation of veterinarians and prescription requirements. At the same time, the country has since 2000 collected substantial data on antibiotic resistance in food animals, humans, and meat. Initially, the country eliminated the use of subtherapeutics at the finishing stage (1998). Producers adjusted their operations to cope with the consequences, and yields stabilized. A ban on usage at the weaning stage, however, led to substantial repercussions, both in terms of a drop in efficiency (few piglets, higher mortality, slower growth) as well as an increase in costs. The increased incidence of disease led to an increase in the volume of therapeutic antimicrobials.

14 _{Wierup, M. The Swedish Experience of Limiting Antimicrobial Use. Proceedings of Agriculture's Role in}

Managing Antimicrobial Resistance Conference, Toronto, Canada, Oct 24–26, 1999. Pg. 1.

15 _{Ibid, 3}

16 _{Swedish Ministry of Agriculture, Forestry, and Fisheries. “Swedish experience of Banning the Use of Anti-}

microbial Growth Promoters,” 2002, http://www.fao.org/docrep/meeting/004/ab457e.htm 17 _Ibid.

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Danish use of animal antibiotics, 1990-2010 (in metric tons)

Source: DANMAP

In terms of the key objective of reducing antibiotic resistance, the results of restricting antibiotic usage have been mixed. For a number of pathogens in animals, resistance to several major classes of antibiotics has decreased (e.g., particularly resistance levels for enterococcus and campylobacter); for others, resistance remains largely unchanged or has increased.

As far as changes in pathogen resistance in humans goes, resistance is in most cases the same or higher, with few exceptions, such as vancomycin resistant enteroccus (VRE), which has dropped since avoparcin was banned for use in animals in 1995.

Danish authorities have found that resistance levels in imported meat and poultry are considerably higher than resistance levels found in domestic meats. The source attribution model used by Denmark to estimate the contribution of animal food sources to human Salmonella infections attributed only one outbreak and five sporadic cases to domestic pork, while attributing 41 cases to imported pork and one to imported turkey meat.18

The Animal Health Institute estimates that if subtherapeutic antimicrobial usage were eliminated, the United States would need an additional 452 million chickens, 23 million additional cattle, and 12 million additional hogs to reach current production levels. Use of antimicrobials is thought by some to be a major factor contributing to healthy large-scale animal agriculture in the United States.

Because young pigs are particularly susceptible to disease, pig farmers are arguably the largest consumer of antimicrobials. Though these antimicrobials are considered by the government as being used for growth

18 _{DANMAP 2010 (Collaboration of the National Food Institute, National Veterinary Institute, Danish}

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enhancement, the reason these products are effective is because they treat incidents of disease in the piglets that occur at subclinical levels. A summary of 1,194 experiments designed to evaluate growth rate increases in hogs from antimicrobial use discovered the following:

 Weanling pigs (15-55 lbs) showed increased growth rates of 16.4% and improved feed efficiency of 6.9%

 Growing pigs (37-108 lbs) had increased growth rates of 10.6% and improved feed efficiency of 4.5%

 Growing finishing pigs (50-195 lbs) increased growth rates by 4.2%, and increased feed efficiency by 2.2%

In addition to these responses, a separate study found that an observation of 1,951 sows showed an increased reproductive efficiency (measured in terms of increased conception rates) of 7% and increased average litter sizes by one half piglet.

In addition, broiler chickens have similarly seen the benefit of about 10% improved feed efficiency through the use of subtherapeutic antimicrobials. Other reasons for growth enhancement include breeding advances, feed ration advances, and better understanding of optimal environments for raising birds. The combined result of these advances has resulted in average growth performance increasing four-fold, from 25 g/day to 100 g/day, in the past 50 years.

The push against subtherapeutic antimicrobials has moved from Europe to the United States. A bill on the subject was submitted to Congress in March of 2010 – and was given backing by the FDA, despite the fact that the agency does not collect the data with which to support its claims.

Moreover, certain market initiatives have also taken place, the most notable of which has perhaps been McDonald’s’ voluntary issuance of strict guidelines for animal food suppliers in reference to their antimicrobial usage.19 _{The policy, which went into effect in 2004, requires that suppliers defined to be in a}

“direct relationship” (those facilities dedicated to producing products for McDonald’s) with the company must certify in writing their compliance with antimicrobial use guidelines and document compliance through regular audits and internal assurance programs. Specific guidelines include:

 all antimicrobial usage must be done under the oversight of a veterinarian;

 all use of antimicrobials also used in the treatment of humans may only be administered after other treatment alternatives have been exhausted;

 all treatments should be limited to the specific treatment of disease control and prevention in animals that are at risk of a specific disease. This includes administering treatment only for as long as it takes to elicit the desired clinical response. Use of antimicrobials should only be used in the correct application for clinical indications; and

 accurate and thorough records must be maintained of all antimicrobial administrations.

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In addition, the McDonald’s policy also forbids the use of antimicrobials that are used explicitly for increasing growth rates. Suppliers who are not considered to be in “direct relationships” with McDonalds have incentives to adhere to the same guidelines in order to be considered more favorably in supply decisions.

Available evidence suggests that restrictions or a ban on the subtherapeutic use of antimicrobials would have a long term impact on production costs. The impact varies substantially, depending on the type of antibiotic, its purpose, and other factors. For instance, in the case of hog farming, the impact is more significant during the piglet stage than during finishing.

US herds and flocks face challenges that are not factors in Denmark, for instance, salmonella and brucellosis, and thus may have higher costs; at the same time, Danish farmers have developed some techniques to help offset the reduced use of antibiotics.

Finally, some medications that are not antimicrobial also help US farmers provide large amounts of food – Ractopamine (Paylean), a beta agonist used in the finishing of pigs, for example, is estimated to increase lean growth by 34% and decrease feed intake by 5.5%.20 _Its elimination could thus have a more substantial impact on supplies, costs and consumer prices.