Animal factories rely heavily on growth-promoting antibiotics. The intensely crowded and sometimes unsanitary conditions of modern industrial livestock production result in stressed animals. Today almost all of the over eight billion cattle, poultry, and swine raised for human consumption in the United States each year receive some type of antibiotic during their lifetime to promote growth. But this reliance on low-level use of antibiotics need not be a requirement for modern animal agriculture. 1 Antibiotics are a class of substances that kill or inhibit the growth of bacteria.
Examples are penicillin and tetracycline.
The first antibiotics were derived from natural sources, but many of today's antibiotics are partically or completely synthetic. Some scientists reserve the term antibiotic for naturally produced substances and use antimicrobial to encompass both synthetic and natural forms. The term antimicrobial also encompasses drugs that kill protozoa. Antibiotics used in animals can make human diseases harder to treat by generating disease-causing organisms that will not respond to antibiotic therapy. One way stems from the fact that animals harbor strains of bacteria in their intestines that cause disease in people.