Antibiotic use in livestock

Source: Alberta Farm Animal Care

Antimicrobials have been widely used in livestock since the 1950’s (1). Food animal production has steadily increased over the years, requiring better disease management on farms. More than 75% of antimicrobials in Canada have been used sub-therapeutically in farm animals to prevent disease and for growth promotion (2,3). In Canada, growth hormones are only approved for use in beef cows (4). All antibiotics used in livestock must meet Health Canada’s standards for human and animal safety (4). For example, maximum levels of antibiotics allowed to be left in food are set at levels much lower than what could pose a health concern (4). The Canadian Food Inspection Agency randomly tests the safety levels of food and if standards are not met then the food will be removed from the food supply (4). As well, most producers work with their veterinarian to determine when it is appropriate to use antimicrobials and determine withdrawal periods so that treated animals or animal products do not enter the food supply until safe to do so (10).

Antimicrobial products have improved health management in modern livestock production (1) by facilitating confinement housing and maintaining higher densities of animals (3). Antibiotic use is beneficial for the agricultural industry because it improves carcass quality, improves feed efficiency, and positively impacts the animal’s welfare by preventing infection and treating disease (1,3). However, the public are concerned about, and seek elimination of, antibiotic use in livestock, particularly for growth promotion, because of the increasing global issue of antimicrobial resistance (5). Antibiotic resistance occurs when a property of bacteria gains the capacity to grow in the presence of antibiotics at levels that would normally suppress or kill the bacteria (8). As antibiotic use has become more common in human and animal health, selection pressure (the extent to which particular characteristics of bacteria are either eliminated or favoured by environmental demands) has increased the ability of bacteria to maintain, accumulate and disperse resistance genes among bacterial populations (1).

Antimicrobials are used in livestock for 4 main reasons: 1) therapeutically to treat sick animals 2) metaphylaxis to treat diseased animals and prevent infection in other animals 3) prophylaxis to prevent infection in animals at risk such as during weaning and transportation 4) growth promotion to improve feed efficiency and productivity (1) . Therapeutic use of antibiotics is crucial for maintaining animal health in intensively reared operations (3). However, poor management can lead to heavy use of antibiotics as a management crutch (3). Furthermore, repeated exposure of animals to low doses of antibiotics creates ideal conditions for the emergence and spread of antibiotic-resistant bacteria (7) . Antimicrobial resistance is a major food safety issue for humans, particularly in Salmonella and E. coli bacterial pathogens (6). Humans can become infected either through direct contact or consumption of contaminated food (6,8). A report from the Center for Disease Control and Prevention states that 2 million people become infected with antibiotic-resistant bacteria (e.g. foodborne pathogens) each year with at least 23,000 deaths annually (6). The issue of antimicrobial resistance is not one to be taken lightly.

In dairy production, 85% of operations use antibiotics therapeutically to treat mastitis, respiratory and diarrheal diseases (1). In beef cattle, antibiotics are given in feed to feedlot cattle and calves during weaning to increase performance and feed efficiency (1). Nontherapeutic use of tetracycline in feedlot cattle has been reported to select for resistant strains of Campylobacter spp. which is a common pathogen that causes foodborne illness in humans (1,3). Also, a survey conducted at 3 feedlots in Saskatchewan, Canada detected E. coli 0157:H7 in 14.2% of the 400 fecal samples and found that 65% were resistant to at least one of the 17 antibiotics tested (1). In poultry, antibiotics are used to treat bacterial diseases such as mycoplasmosis and salmonellosis, which cause significant economic losses to the industry (1). The increased demand for meat has caused producers to use antimicrobials therapeutically and as growthpromotants, which places even greater selection pressure for antibiotic resistance (7). The Centre for Disease Control and Prevention (CDC) urges the need for proper management of antimicrobial use in livestock but states that the number one contributing factor to the development of antibiotic resistance is the misuse/overuse of antibiotics within human populations (12). Similarly, Adjiri-Awere and Van Lunen (2005) propose that antimicrobial resistance in humans likely resulted from prescribed antibiotics. Furthermore, Adjiri-Awere and Van Lunen (2005) suggest there is no direct link between feeding antibiotics sub-therapeutically to animals and negative health effects in humans.

There are 4 categories of antimicrobials 10:

1. 1. ‘Very High Importance’ – antimicrobials used to treat serious human infections

1. 1. ‘High Importance’ – antimicrobials of intermediate concern in human medicine

1. 1. ‘Medium Importance’ – antimicrobials rarely used in human medicine to treat serious infections (e.g. tetracycline to treat acne)

1. ‘Low Importance’ – antimicrobials not used in humans at all (e.g. ionophores)

Most antimicrobials used in Canadian farm animal production are of low importance in human health, meaning they are not used in human medicine (10). Antimicrobials of greatest concern to humans are the ‘Very High Importance’ antimicrobials which are only used in livestock as a last resort for infections that are not responding to lower drugs (10). A study funded by the Beef Cattle Research Council found that antibiotics used most widely in the Canadian beef industry are never used in human medicine (10). The reduction or elimination of sub-therapeutic use of antibiotics in animal production may have negative effects on animal welfare, nutrient utilization, and economic sustainability (8). For example, Denmark banned the use of antibiotics as growth promotants(AGPs) in finisher pigs in 1998 (11). They found that there was a significant impact on animal health and realized that the antimicrobials were preventing a lot of diseases, not just enhancing growth promotion. They also found that the AGP ban did nothing to improve human health (i.e. resistance levels nor rates of food-borne illness decreased; 11). If Canada or the United States were to ban antimicrobial use the impacts would be much greater as Denmark is a small country.

Alternatives to antimicrobial use in animals for growth promotion and disease prevention are being developed, however many of the alternatives are not yet commercially available (6,8) because scientific evaluation must first demonstrate that there are no harmful effects on human and animal health or on the environment (9). Alternatives include: probiotics (live microbial supplements that improve microbial balance in the intestines); prebiotics (non-digestible food ingredient that promotes beneficial microbial growth in the intestines); nutraceuticals (e.g. herb extracts, spices, aromatic oils); acidifiers (e.g. organic and/or inorganic acids); minerals (e.g. Zinc, Copper); egg yolk antibiotics (antibody content of a hen’s egg is 20x greater than the antibody content of a cow’s colostrum;8). For alternatives to be as successful as sub-therapeutic levels of antibiotics, a sound health management plan is essential that reduces stress on animals. Overall management practices are important as well such as improved sanitation, more careful group mixing, low-stress weaning, and low-stress handling.

And make sure to take a look at our

fact sheet on how antibiotics are

used in the livestock industry!

References

1. Mathew, A. G., Cissell, R., and Liamthong, S. 2007. Antibiotic resistance in bacteria associated with food animals: a United States perspective of livestock production. Foodborne Pathog, Dis. 4:115-133.
2. Farm Credit Canada. 2016. https://www.fccfac.ca/en/news/2016/Jul/06aa47a4d9c4403cb7c3acf97f72a548.html (Accessed 16 June 2017.)
3. Tollefson, L., and Miller, M. A. 2000. Antibiotic use in food animals: controlling the human health impact. J. AOAC International. 83:245-254.
4. Eat Right Ontario. 2016. Hormones and antibiotics in food production. https://www.eatrightontario.ca/en/Articles/Farming-Food-production/Hormonesand-antibiotics-in-food-production.aspx (Accessed 16 June 2017.)
5. Beef Magazine. 2005. The antibiotics argument. http://www.beefmagazine.com/mag/beef_antibiotics_argument (Accessed 16 June 2017.)
6. Diarra, M. S., and Malouin, F. 2014. Antibiotics in Canadian poultry productions and anticipated alternatives. Frontiers in Microbiology. 5:1-15.
7. Van Boeckel, T. P., Brower, C., Gilbert, M., Grenfell, T., Levin, S. A., Robinson, T. P., Teillant, A., and Laxminarayan, R. 2015. Global trends in antimicrobial use in food animals. PNAS. 112:5649-5654.
8. Adjiri-Awere, A., and Van Lunen, T. A., 2005. Subtherapeutic use of antibiotics in pork production: risks and alternatives. Can. J. Anim. Sci. 85: 117-130.
9. Yirga, H. 2015. The use of probiotics in animal nutrition. J. Prob. Health. 3: 1-10. doi:10.4172/2329-8901.1000132
10. BCRC. Beef Cattle Research Council. 2017. Antimicrobial resistance. http://www.beefresearch.ca/research-topic.cfm/antimicrobial-resistance11#cattleconcerns (Accessed 16 June 2017.)
11. Beef Magazine. 2005. The antibiotics argument. http://www.beefmagazine.com/mag/beef_antibiotics_argument (Accessed 16 June 2017.)
12. Meat Mythcrushers. 2014. Myth: animal agriculture is the biggest contributor to antibiotic resistance. http://www.meatmythcrushers.com/myths/myth-animalagriculture-is-the-biggest-contributor-to-antibiotic-resistance.html (Accessed 21 June 2017.)