Antibiotics are commonly used in U.S. livestock to promote growth, prevent diseases and treat sick animals, but the use of antibiotics are being challenged consumers and regulatory agencies.

According to a story on Choicesmagazine.org, a website by the Agricultural & Applied Economics Association, the U.S. Food and Drug Administration (FDA) estimates that 32.2 million lbs. of antibiotics were sold for use in animals in 2012, more than four times the 7.3 million lbs. of antibiotics sold for human use in 2011. Antibiotics are used primarily in intensive swine, poultry, and feedlot cattle systems, with limited use in dairy cows, sheep and companion animals.

The extensive use of antibiotics in livestock comes at a cost: it contributes to the increase in drug-resistant pathogens in animals that can potentially be transmitted to humans and negatively impact human health, even if the magnitude of the risk to human health is still. Concerns about increasing antibiotic resistance led to bans on antibiotics for growth promotion (AGPs) in the European Union in 2006. In the United States, AGPs are not banned, but the FDA recently issued guidelines for the industry to voluntarily withdraw medically important antibiotics from growth promotion. For policy makers, the challenge is to evaluate the benefits and costs of animal antibiotics to society. What is the economic value of antibiotics to the livestock industry versus the potential health cost of increasing resistance levels? What are the potential productivity and economic effects of a ban on AGPs for U.S. meat producers and consumers?

The major inputs in food animal production — feed, labor and capital — can be improved on some operations by feeding antibiotics. AGP use can enhance the growth rate and the feed conversion ratio, the rate at which animals convert feed into weight gain, and it can increase labor or capital productivity by substituting for hygiene management in animal housing or transportation. Using AGPs could also reduce variability in animal weights and sizes, avoiding financial penalties at markets for animals outside the range suited for mechanized processing.

The growth response to antibiotics may have decreased over the past 30 years for several possible reasons. First, the growth response to antibiotics is less important when animal nutrition, hygiene, genetics and health are optimal. The relative improvement in the growth rate resulting from supplementing the diet of pigs with antibiotics has been shown to be inversely related to the growth rate of animals not being fed antibiotics. With changes in the livestock industry over the past 30 years, all of these factors have improved. Second, increasing levels of resistance in animals could be diminishing the overall effectiveness of AGPs, although data are lacking to evaluate this hypothesis.

In Denmark, which has an export-oriented, market-driven, and intensive production system, the use of AGPs was banned in finishing pigs in 1998 and in weaning pigs in 2000. The termination of AGPs had no major effect on productivity or feed efficiency in finishers but resulted in some loss of productivity in weaners. Long-term swine productivity improved markedly between 1992 and 2008, suggesting that the ban on AGPs did not harm long-term productivity. The effects of the ban on AGPs on antibiotic consumption are mixed. Between 1997 and 2008, the total consumption of antibiotics in the Danish swine production industry decreased from 81.2 mg/kg of pork produced to 48.9 mg/kg of pork produced. Following the AGP ban, total antibiotic use was at its lowest level in recent years in 1999. However, the therapeutic use of antibiotics increased and the total antibiotic consumption for animal production increased by 36% during the period 2001 through 2009. This led the Danish government to impose new restrictions on producers’ uses of antibiotics, and total use has started decreasing again after 2009.

If the benefits of AGPs (in terms of increased productivity) have diminished, then it becomes reasonable to be cautious and avoid the potential public health costs (in terms of increased resistance) rather than wait for a complete understanding of the ecology of gene flow between the animal, the environment and human reservoirs. The use of antibiotics should principally be the last resort rather than a substitute for biosecurity, hygiene and other good practices. Antibiotics are not needed to promote growth, but they are essential to treat infectious diseases and maintain animal health. Since new antibiotic classes will likely not be available to veterinary medicine, it is in the best interests of food animal producers to preserve the effectiveness of existing veterinary antibiotics through antibiotic stewardship. The challenge for policy makers is to find that balance between allowing use of antibiotics to control animal diseases and restricting their use to limit the emergence and spread of antibiotic resistance.

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