Antimicrobial growth promoters and their effects on swine fecal bacterial communities
LE3 .A278 2017
Bachelor of Science
While antimicrobial growth promoters (AGPs) are widely used in North American animal production, there is a limited understanding of how they affect the animals which receive them. It is commonly claimed that animals fed AGPs have improved growth performance, reduced mortality, and improved overall herd health compared to animals not fed AGPs. These benefits are also commonly claimed to result from alterations of animal gut bacterial communities. More recently it has been suggested that AGPs work primarily as immune modulators, reducing host immune reactions in the gut, and rechanneling this energy into animal growth. The purpose of this research was to determine if AGPs alter fecal communities in swine and assess their possible immunomodulation effects in pathogen-challenged pigs. The experiment was a two block repeated design where swine in the first block were split into three treatment groups (control, tylosin-fed, chlortetracycline-fed). Swine in the second block were treated the same but were challenged at the study midpoint with a cocktail consisting of various species of Salmonella. Fecal samples were collected every week and DNA was extracted. The extracted bacterial DNA was amplified using polymerase chain reaction (PCR) using primers that would target the V1-V2 region of the 16S rRNA gene. Denaturing gradient gel electrophoresis (DGGE) was used to fingerprint the fecal communities, and these fingerprints were analyzed by ordinal analysis. Differences in fecal communities in swine fed AGPs were observed in Trial I, however no differences in fecal communities in swine fed AGPs were observed in Trial II. No effects due to pathogen challenge were observed. A temporal change was observed in the gut communities, although this was independent of any treatment. The microbiota of the gut changes during growth and development in all mammals. This study indicates that AGPs do not alter bacterial fecal communities in swine, and raises questions regarding hypotheses purporting to explain their underlying mechanism of action.
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