Study first of its kind to look at the collateral effects of in-feed antibiotic use in farm animals

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Antibiotics in pig feed increased the number of antibiotic -resistant genes in gastrointestinal microbes in pigs, according to a study conducted by Michigan State University (MSU) and the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS).

Published recently in the Proceedings of the National Academy of Sciences, the comprehensive study, co-authored by MSU AgBioResearch scientist James M. Tiedje, focused on understanding the effects of conventional in-feed antibiotics use on U.S. farms.

For decades, many producers of pigs, chickens and other farm animals have used antibiotics not only to protect their livestock from disease but also to boost growth rates and enhance feed efficiency,  a measure of how well animals convert feed into weight gains.

“Scientists don’t know precisely how antibiotics enhance growth rates and feed efficiency, but they are concerned that on-farm use of these medications may contribute to the development of strains of microbes resistant to conventional antibiotics, strains that are potentially harmful to humans and animals,” said Tiedje, an MSU university distinguished professor of microbiology and molecular genetics and crop and soil sciences.

“The growth of antibiotic resistance in pathogens is a huge challenge for society around the world,” Tiedje said. “Studies to understand what contributes to the spread and what interventions can help control the problem are vital.”

Additional findings include:

  • Both diversity and abundance of antibiotic-resistant genes increased in the intestinal microbial communities of the pigs treated with antibiotics. Longer term studies are needed.
  • Some of the genes found in the treated pigs were unexpected and usually linked to antibiotics not used in the study.
  • Microbial genes associated with production and use of energy by microbes increased in abundance in the antibiotic-fed pigs. This finding may shed light on how antibiotics increase livestock growth and feed efficiency.
  • E. coli populations increased in the intestines of the treated pigs. Further study is needed to clarify this observation.

According to the USDA, this study is the first of its kind to look at the collateral impacts of in-feed antibiotic use in farm animals using a comprehensive approach to detect shifts in the function and the makeup or membership of the microbial community in the model animal’s gastrointestinal tract.

Other MSU researchers involved in the project are: Tim Johnson, crop and soil sciences doctoral student; Robert Stedtfeld, civil and environmental engineering research associate; Woo Jun Sul, crop and soil sciences doctoral student; Tiffany Stedtfeld, civil and environmental engineering technical aide; Benli Chai, information technologist, Center for Microbial Ecology; James Cole, assistant professor at the Center for Microbial Ecology; and Syed Hashsham, professor of civil and environmental engineering.

Funding was provided by the MSU Environmental Science and Policy Program Initiative on Pharmaceuticals in the Environment, the ARS  and the National Institutes of Health, and through the Alliance for the Prudent Use of Antibiotics Program on Reservoirs of Antibiotic Resistance.

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