Why are antibiotics used in animal production?

Antibiotics are medicines useful for controlling and preventing disease in livestock. Proper use can keep animals healthy, control the spread of diseases between herds, help animals gain weight and prevent the spread of diseases from animals to humans.

In the U.S., many livestock producers give their animals low doses of certain antibiotics to improve overall health and help animals gain weight. This is also called "subtherapeutic" use because instead of curing a specific disease, the antibiotics are used to improve overall growth and health.

Learn more about antibiotic use in livestock

Animals play host to many kinds of gut microbes, which are bacteria that live in the stomach and help break down food. Though many gut microbes aid in digestion and immune response, they also compete with animals for nutrients. Antibiotics in animal feed can reduce this competition and help an animal gain weight more efficiently. Low doses of antibiotics can also ward off "subclinical infections" that stress the animal's immune system and slow growth.

Use of growth-promoting antibiotics is one way livestock producers meet global demand for food. In 2002, Dr. Gary Cromwell, a professor of swine nutrition at the University of Kentucky, published a paper showing that antibiotics dramatically improved pig growth. Cromwell analyzed the results of more than 1,000 growth experiments in swine over a 25-year period. In young pigs, antibiotics improved the growth rate by an average of 16.4%.

What is antibiotic resistance?

It is widely accepted that bacteria can become resistant to antibiotics over time. In a large population of bacteria, there may be a few individuals with genes that allow them to resist antibiotics. When exposed to antibiotics, these resistant bacteria can survive while the antibiotic-susceptible individuals die off. These resistant bacteria live to pass their antibiotic-resistant genes to their offspring. Over time, more and more individuals in the population have the resistant gene. This cycle can lead to strains of antibiotic-resistant disease.

Recently there has been concern that by feeding antibiotics to animals, there will be an increase in antibiotic resistance, especially in humans. This could lead to a decrease in the helpfulness of lifesaving antibiotics. To help with the increased worry about the use of antibiotics in livestock production, there has been a call for the judicious use of antibiotics. Judicious use means that the use of antibiotics would be more controlled by veterinarians and there would be a decrease over time in the use of antibiotics not used for the treatment of illnesses.