Subtherapeutic antibiotic use in swine

Antibiotics are commonly used in commercial swine production in the United States and around the world. They are used for disease treatment, disease prevention and control, and growth promotion. When used for growth promoting purposes, antibiotics are given at low concentrations for long periods of time. Low concentration of antibiotics, also referred to as (STA), are given as feed and water additives which improve daily weight gain and feed efficiency through alterations in digestion and disease suppression. Additionally, the use of STA in swine results in healthier animals and reduces the “microbial load” on meat resulting in an assumed decrease in potential Foodborne illness risk. While the benefits of subtherapeutic antibiotic administration are well-documented, there is much concern and debate regarding the development of bacterial antibiotic resistance associated with their use.

This is a specific case of the more general practice of .

Currently, there appears to be a lack of reliable data associated with the amount of antibiotics used in livestock production. In 2001, the Union of Concerned Scientists (UCS) published that 24.6 million pounds of antibiotics are used annually for growth promotant purposes. This, they claimed, represented 70% of the antibiotics produced annually in the United States. However, groups such as the Animal Health Institute have taken issue with this figure, accusing the UCS of using questionable methods and assumptions. Listed in Table 1 are the specific types of antibiotics used in swine disease treatment, prevention and growth promotion and their importance in human medicine.

Table 1- Commonly used antibiotics in swine production and their relative importance in human medicine. With regard to human medicine importance, FDA ranks antibiotics as “critically important” (“critical” in the above table), “highly important” (“high” in the table), or “important.” The ranking is based on five criteria from the most important (it is used in treating pathogens that cause foodborne disease) to the least important (there is difficulty in transmitting resistance across genera and species).

Bacterial antibiotic resistance is a process that can occur when bacteria are exposed to STA administration. When a population of bacteria that resides in a hog are exposed to a particular antibiotic for growth promotant purposes, the bacteria that are susceptible to the drug die while the organisms that are resistant will not be affected and will continue to replicate, resulting in a higher proportion of resistant organisms. It has been shown that resistance to antibiotics develops in animals that are fed subtherapeutic doses of antibiotics for growth promoting purposes. Certain bacteria that have the potential to cause human illness, such as Salmonella, that naturally reside in the swine gastrointestinal tracts are constantly exposed to antibiotics. With time, these bacteria become resistant to that class of antibiotics. There is great concern regarding the probability of subtherapeutic antibiotic use in swine causing treatment failures in human medicine.

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