Pros

• Animals receiving antibiotics in their feed gain 4% to 5% more body weight than animals that do not receive antibiotics.

• Antibiotics are used for treatment of animal disease and/or disease prevention.

• Livestock treated with antibiotics live longer than those who are not treated.

• The shelf life is extended for meat, poultry, eggs, and dairy products when treated with antibiotics.

Cons

• Widespread antibiotic use has led to multidrug-resistant pathogens.

• A joint National Research Council/Institute of Medicine panel has concluded that antibiotic-resistant human diseases have "clearly occurred" due to bacteria from antibiotic-treated livestock.

• 1970s: High doses of antibiotics given to chickens leads to resistant Salmonella strains found in both meat and eggs. In 1983, this phenomenon was also demonstrated for low-level use of antibiotics in livestock.

• Fluoroquinolones used in livestock animals can contribute to increased resistance in foodborne bacteria which can then infect humans. For example, the Minnesota Health Department found that 70% of the chicken meat samples they collected were contaminated with campylobacter, and that 20% of the infected meat carried a resistant strain.