Studies assess economic, environmental effects of antimicrobial drug use on hog farms

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The use of subtherapeutic doses of antimicrobial drugs may drive down hog prices and lower profits for the entire hog industry at the same time that individual hog producers gain, a new government report says.

According to the report by Kenneth H. Mathews Jr of the USDA's Economic Research Service, the hog industry as a whole could have increased its net gain by about $7 million in 1999 if this type of antimicrobial use had been banned.

Using past studies and general economic data from the swine industry, Mathews arrived at this figure by developing a model simulating what would have happened in 1999 if none of the nation's hog farmers had used subtherapeutic doses of antimicrobials. The conclusions were based on the assumption that one-fourth of swine farmers used antimicrobials that year, a figure the author calls conservative.

Antimicrobials boost production and increase supply, thereby decreasing prices. Had they not been used in 1999, the model predicted that the average price of hogs for the year would have gone up to $34.80 per hundredweight from $34.02.

Although the price boost would have resulted in larger profits, feed costs also would have increased for producers who ceased their use of antimicrobials. The drugs increase feed efficiency, so halting their use would require producers to feed animals more to attain the same weight. However, only the producers who used antimicrobials would have had to purchase an increased amount of feed if the antimicrobials were not used, even though price increases affect all producers. Those particular producers—the fourth of all swine farmers—would have lost a total of $45.5 million, even as the industry increased profits overall.

This hypothetical "thought experiment," the report says, could also be influenced by factors such as the increase in feed costs likely if demand for feed increased and the veterinary costs associated with the use of antimicrobials.

The report also looks at past studies of the economic impact of bans on the use of subtherapeutic doses of antimicrobials in livestock—most of which predicted higher prices for both producers and consumers under a full or partial ban. Summarizing the findings of earlier studies, Mathews concludes "a ban against using antimicrobial drugs in livestock production would come with a cost." Neither these studies, nor Mathews' model, addressed the effects of antimicrobials on resistant bacteria or human health.

The Animal Health Institute hailed the report as providing valuable perspective on the debate over antimicrobial use in food production.

"Antibiotics are important tools in the toolbox farmers use to keep animals healthy and to efficiently produce food," said Alexander S. Mathews, president and CEO of AHI, in a statement. "Consumers benefit from a safe, wholesome, abundant, and more affordable food supply."

As the USDA calculated the economic effects of subtherapeutic antimicrobial use, a group of researchers at the University of Illinois at Urbana-Champaign released a study assessing some of the environmental effects of feeding the drugs to livestock.

Roustam I. Aminov, a visiting professor of animal studies, led a team that identified the genes of bacteria resistant to tetracycline in groundwater about a sixth of a mile from two swine facilities that use antimicrobials. Using a polymerase chain reaction assay, the researchers identified the genes and found them similar to resistance genes in the gastrointestinal tracts of pigs.

"The elevated frequencies of these genes in the environment surrounding the farms were consistent with the hypothesis that this occurrence was the result of gene flow from the animals," Aminov said in a statement.