Overuse of Antibiotics in Livestock Leading to Antibiotic Resistance

Vanessa Sheehan – Animal Science

Caley Earls – Natural Resources

Brett Duran – Building Construction Technologies

Industrial livestock farms rely on antibiotics as a growth additive for production (Akoury, 2015).

Antibiotics are very common to come by in the average person’s life. People rely on antibiotics to treat many different bacterial infections that they may contract. But what happens when antibiotics do not work? Many families, including the Wade family, know the horrible answer to that question. Young Brock Wade was a very happy, active, and healthy 9-year-old boy who had gotten hurt while playing outside. He only had a few minor cuts and bruises, but this led to a raging infection that almost took Brock’s life. It began with Brock complaining of a little arm pain, then excruciating arm pain and being unable to sleep. He then lost consciousness that resulted in him being rushed to the hospital. Many tests and false diagnoses later, it was discovered that Brock had contracted Methicillin-resistant Staphylococcus aureus (MRSA). The infection was so advanced that it had spread to his arm, heart, and lungs. Brock was put on multiple antibiotics in an attempt to kill off the infection, but in the end had to undergo many invasive surgeries during a month-long hospital stay in order to treat the MRSA infection. Luckily for Brock and his family, he did make a full recovery (Bailey-Wade, 2015).

Brock had contracted MRSA from a cut on his leg, not from eating contaminated meat. However, concentrated animal feeding operations (CAFOs) use antibiotics to enhance growth in their livestock in order to produce more meat products and generate more revenue. The problem is, the great overuse of antibiotics on these factory farms generate antibiotic resistant bacteria (ARB), including MRSA. A study in Denmark had shown that multiple MRSA infections in humans had been contracted from food animals. This study has gotten many scientists to believe that this is concrete evidence for antibiotic use in livestock posing a great threat to human health (Bottemiller, 2013).

Concentrated animal feeding operations, commonly referred to as CAFOs, are industrial livestock farms that raise animals for consumption where the animals confined for at least 45 days during the year and discharges waste into a water supply in a particular manner (Hribar, 2010). CAFOs rely on antibiotics as growth promoters to enhance their production of livestock as a feed additive and for therapeutic uses, including illness and disease. The addition of antibiotics to the feed increases livestock weight, decreases disease, and allows the livestock to more efficiently converse their feed (Boyd, 2001). The antibiotics function by reducing bacteria in the intestines of livestock; the bacteria affected include normal intestinal bacteria and harmful intestinal bacteria. These bacteria compete with the host for nutrients from the feed and cause diseases, respectively (Wegener, Aarestrup, Jensen, Hammerum, & Bager, 1999). The removal of these bacteria allows the livestock to greater feed efficiency, which allows for weight gain and decreased disease rates. The heavy reliance on antibiotics by CAFOs leads to antibiotic resistant bacteria (ARB) – bacteria that evolved resistant against the antibiotics commonly used to treat them, making use of these antibiotics ineffective as a treatment method for disease or infections caused by the bacteria.

Antibiotics have been found to improve the feed conversion ratio, the ratio of how much feed is given to the animal and how much food they actually produce, in livestock and ultimately lead to weight gain. There is no clear cut answer as to how the antibiotics on a molecular level, however it is theorized that the antibiotics affect the bacteria in the gastrointestinal tract of the animal which leads to the weight gain. It is also theorized that the cytokines that are released from the immune response of the antibiotics lead to the release of the catabolic hormones that ultimately lead to higher muscle weight (Hughes & Heritage, 2001). The overuse of antibiotics on CAFOs lead to negative health impacts though antibiotic resistance, and antibiotics should no longer be used as a growth promoter within these facilities.

The use of antibiotics in animal feed as a growth additive leads to a greater presence of ARB. According to the report “Antibiotic Resistance Threats in the United States, 2013” by the Centers for Disease Control and Prevention (CDC), the leading cause of antibiotic resistance is the use of antibiotics, with antibiotics commonly used in animal practices as growth promoters (CDC, 2013). Overuse of antibiotics for sub therapeutic uses may lead to higher incidences of antibiotic resistant genes (Economides, Liapi, & Makris, 2012). Chambers et al. (2015) found that Ceftiofur, a common antibiotic used for dairy cattle, results in a high occurrence of antibiotic resistant genes found in cattle feces. Antibiotics, specifically Cephapirin, lead to ARB in the feces and urine of dairy cattle (Ray, Knowlton, Shang, & Xia, 2014).

ARB spread through groundwater and surface water contamination, meat products, and manure from CAFOs. The CDC published a fact sheet to warn civilians of the threats of antibiotic resistance from farms and how they may be affected; they credit the spread of bacteria from farms through animal products and contamination of water, soil, and environment from feces (CDC graphic illustration, 2015). Givens et al. (2016) concluded in their study of manure runoff that areas near CAFOs have higher levels of ARB. Manure from CAFOs, commonly used in agriculture, contains unmonitored ARB (Chambers et al., 2015).

Economides et al. (2012) investigated the presence of antibiotic resistant Salmonella and Escherichia coli strains found in groundwater near CAFOs in Cyprus. Of their groundwater samples for each resistant bacterium, 3.1% of Samonella samples and 33.3% of E. coli tested positive for antibiotic resistance (Economides et al., 2012, p. 394). 88% of their samples came from CAFOs in 2 districts in Cyprus, where more than 80% of the country’s cattle population exists (Economides et al., 2012, p. 395).

West, Liggit, Clemans, and Francoeur (2011) found that ARB incidences increase near CAFOs by testing the density of the fecal coliform bacteria, commonly found in the guts of warm-blooded animals and humans. They tested 830 fecal coliform isolates for resistance against 5 antibiotics, finding that 98.3% of isolates showed resistance to one or more antibiotic (West et al., 2011, p. 479). The authors observed a greater proportion of resistance to more than one antibiotic near CAFOs site, where 41.6% of agricultural impaired sites near CAFOs showed resistance to multiple antibiotics and only 16.5% of agricultural unimpaired sites showed multi-antibiotic resistance (West et al., 2012, p. 485).

Graham, Price, Evans, Graczyk, and Silbergeld (2009) studied how houseflies – known dispersers and transmitters for bacterial infections – spread antibiotic resistant Enterococcus spp. and Staphylococcus spp. Their study revealed that if house flies feed on livestock excrement at CAFOs, they may ingest ARB or receive the bacteria through surface contamination. The flies may then spread ARB to areas outside the CAFO or directly to humans through physical contact, defecation, or regurgitation (Graham et al., 2009).

Antibiotic overuse in livestock causes antibiotics to be less effective in humans when used for the treatment of infections and diseases (Kaufman, 2000). In the United States alone, over 2 million people suffer from antibiotic resistant infections, where at least one antibiotic that could treat the infection is now ineffective. 23,000 of these 2 million people die annually from these infections with even more people dying indirectly from their infections (CDC, 2013, p. 11). Humans are at a high risk to come into contact with ARB through their everyday meat products and produce that may be contaminated. Of all infections caused by ARB, 20 percent are tied to consumption of food containing resistant bacteria (CDC graphic illustration, 2015).

Manure on pigs has been found to contain the hepatitis E virus, including a strain specific to humans (Givens et al., 2016). Ceylan, Berktas, and Agaoglu (2008) focus on antibiotic resistant Aeromonas species in livestock feces as a possible hazard to human health, posing risks to immunocompromised humans. According to their research, humans are at risk through swimming in or drinking contaminated water, such water near CAFOs. The study by Economides et al. (2012) led the authors to believe that the observed concentrations of ARB in the groundwater could cause Salmonella poisoning and gastrointestinal infections. West et al. (2011) acknowledge that increased fecal coliform densities in water creates a greater risk to humans for developing a disease from the bacteria (West et al. 2012).

In 1985, an outbreak of Salmonella across 5 states affected nearly 200,000 people. Scientists at the CDC traced the outbreak back to Hillfarm Dairy in Melrose Park, Illinois. With more than 16,000 cases reported, they discovered that the Salmonella strain was resistant to multiple antibiotics and believed that it originated from the cows on the dairy farm. The CDC research on the outbreak revealed that people taking antibiotics who drank the milk became sicker than those who only drank the tainted milk; the antibiotics they took eliminated healthy gut bacteria, giving the Salmonella bacteria an advantage to thrive in their systems. The resistant Salmonella strain survived through pausteration at Hillfarm Dairy. Up to 12 deaths resulted from this outbreak and put the country into a panic over antibiotic resistance (Van, 1987).

The CDC believes that using antibiotics as growth promoters in animal practices is unnecessary and should be “phased out” (CDC, 2013). The U.S. Food & Drug Administration (FDA) believes medically important antibiotics should be voluntarily phased out and set forth guidelines for drug sponsors who want to end production of their medically important drugs for animal purposes (FDA, 2013). The FDA suggests three claims of “antibiotic free” production for livestock markets: 1) raised without antibiotics, where the livestock receives no antibiotics during their lifetime; 2) raised without sub therapeutic antibiotics, where livestock only receive antibiotics for the treatment of illness or disease; and 3) no detectable antibiotic residue, where livestock may receive antibiotics during production and placed on the market with proper labeling provided analysis of antibiotic resistance (FDA, 2002).

We propose that CAFOs limit antibiotic use to therapeutic reasons only, such as illness and disease. If CAFOs do not rely on antibiotics to enhance growth in livestock, then the spread of ARB through livestock will decrease and pose a lesser risk to human health. By no longer using antibiotic as a feed additive, CAFOs can label themselves as “antibiotic free” farms. Consumer demand for antibiotic free animal products only increases in the market, making movement to antibiotic free styles farms the logical decision for CAFOs (NRDC, 2015). 86 percent of consumers seek antibiotic free meats in their local supermarkets, and 61 percent will pay at least 5 cents more per pound for antibiotic free meat (Consumer Reports, 2012, p. 3).

A number of restaurant chains and animal product suppliers, including McDonald’s and Tyson Foods, claimed they stopped using medically important antibiotics in their practices. This change in production aligned with an increase of sales: in the past 3 years, sales for antibiotic free animal products rose 25 percent (NRDC, 2015, p. 2). An economic assessment by Graham, Boland, and Silbergeld (2007) revealed that growth producing antibiotics increases the value of a chicken by $0.0016 but increases production costs by $0.0069 based on the Delmarva Peninsula data set. Using the North Carolina data set, the net value of a chicken raised by $0.0048 to $0.0135 when growth promoting antibiotics are removed (Graham et al. 2007, p. 85). As the market continues to grow, antibiotic free farms will become more economically feasible.

The United States would not be the first to end nontherapeutic antibiotic use in livestock. The European Union (EU) officially banned the use of all types of antibiotic growth promoters (AGPs) on CAFOs in 2006. Records dating back to 1986 show the first ban of AGPs in Sweden. Since then, the countries of the EU have been slowly working to ban the use of AGPs entirely. The US can use the findings and experiences of the countries in the EU and learn from them. Following the ban in Sweden, researchers found a 66% percent decrease in the sales of antibiotics used in livestock. This could potentially cause economic problems by hurting the pharmaceutical market. They also found that livestock, specifically pigs and poultry, developed inflammation in the intestines resulting in diarrhea and dysentery following the ban (Cogliani, Goossens, & Greko, 2011, p. 276).

The ban in The Netherlands resulted in their country learning that, on top of the ban, they needed to take more measures to keep antibiotics use at a minimum. They found that following the ban, antibiotic usage did not decrease because they lacked proper animal husbandry practices and the government improperly regulated the antibiotic therapeutic use initially (Cogliani et al., 2011, p. 277). The US can learn from this by implementing strict guidelines for how to use antibiotics only therapeutically at the start of the change. They can also regulate health and nutritional protocols on livestock to ensure that therapeutic antibiotic use is minimal.

When Denmark banned the use of AGPs, they saw a 90 percent decrease in the use of antibiotics in livestock, the other ten percent is the minimal use of antibiotics for therapeutic reasons (Cogliani et al., 2011, p. 276). They also found an increase in pigs developing diseases, such as Lawsonia intracellularis and post-weaning multisystemic wasting syndrome (Cogliani et al., 2011) that cause diarrhea in both cases plus circulatory and respiratory problems in the latter (Segalés & Domingo, 2002).

Farmers would most likely have a problem with the changes that would be imposed on their farm. They would not be for these changes, unless they could see some benefits to making them. One large benefit would be the ability to change their labels. A farmer would not be administering antibiotics unless the animal was in need of them. With our proposal, animals would be treated with NGPs instead of antibiotics which allows them to use the label “antibiotic free”. Farmers cannot say antibiotic free if they have a sick animal and they choose to treat them with antibiotics. However, there are labels that say “no sub therapeutic antibiotics added” which means that they were only given antibiotics as a treatment instead of as growth promoters. (Farm Sanctuary Report, p. 14). Considering the general population is leaning towards wanting “antibiotic free” meat, these labels could lead to an increase in sales of meat coming from these farms, so farmers would be making more money.

Farmers would also be concerned about the changes in the timeline of their production cycle. Phytogenic feed additives (PFAs) are a plant based growth promoters that can be used as an alternative to antibiotics. A study by Wati, Ghosh, Syed, and Haldar (2015) measured the efficacy of PFAs compared to antibiotics. They found that the broiler chickens that were given the PFAs had a high body weight gain and feed conversion efficiency, which is the ability of the animal to convert their feed into products such as meat or milk. The essential oils within the PFAs increased the production of the digestive enzymes which led to more nutrients being digested. The PFAs had an almost as efficient feed conversion ratio of 1.632 compared to the antibiotic treated chickens which had a ratio of 1.729 (Wati et al., 2015, Table 2). The PFAs were roughly as effective as the antibiotics were as growth promoters. This means that farmers would not experience much of a change in their production cycle when using this animal and environmentally friendly alternative.

Some ask why we chose to completely get rid of antibiotics on CAFOs instead of just focusing on manure management or other alternatives. We are not proposing completely getting rid of antibiotics on farms, but just restricting them to necessary use so that we can limit the creation and spread of ARB. As for manure management, many farmers use the manure produced by their livestock as fertilizer so they can save money. In the studies from both Chambers et al. (2015) and Ray et al. (2014), they had discussed the idea of focusing on manure management by treating the manure before it is spread on pastures. While this may be an effective alternative, most CAFOs are concerned about costs and efficiency when it comes to changes on their farm. If they go the route of continuing to use antibiotics as growth promoters and then treating the manure to eliminate ARB, they would be spending even more money. That method would mean they would spend the same amount on antibiotics and then an additional amount to treat the manure, and would be much more time consuming than just taking the manure straight to the pastures.

Another potential alternative to our method would be to just eliminate CAFOs entirely. While this is seems like an easy and simple solution, this can create more problems than solutions. The purpose of CAFOs are to raise livestock from birth to slaughter in a fast and efficient manner. This way large amounts of meat and other products that come from livestock can be produced. This is very important for the increasingly large population of the United States. A growing population requires that the food supply grow as well. Eliminating CAFOs altogether would greatly reduce the food supply in the US. Small, independently owned farms simply cannot produce enough meat products in order to compensate for the amount missing from CAFOs. Also, the mass production of the food from CAFOs allow for the meat, eggs, and dairy products cost less to the consumer. CAFOs can also potentially boost the economies in the areas local to the farm by increasing job opportunities and bringing more revenue to the towns (Hribar, 2010, p. 2).

Antibiotic overuse on CAFOs lead to the creation of ARB. These ARB live in and are passed through livestock and can end up contaminating groundwater and meat products. ARB can lead to life threatening infections in humans and therefore have the potential to negatively impact human health. A great way to prevent humans coming in contact with ARB is to limit the use of antibiotics in livestock that are bred for human consumption. A lot of the meat that humans consume are products of CAFOs. Therefore, if CAFOs join the “antibiotic free” movement, they could greatly reduce the possibility of humans contracting ARB.



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