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Theses and Dissertations

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Browsing Theses and Dissertations by Subject "antibiotic resistance"

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    The effects of a Saccharomyces cerevisiae fermentation product on liver abscess prevalence, microbiomes, and resistomes of cattle raised to produce natural-branded beef
    (Colorado State University. Libraries, 2018) Huebner, Katherine Louise, author; Morley, Paul, advisor; Belk, Keith, committee member; Metcalf, Jessica L., committee member; Sischo, William M., committee member
    Use of antibiotics in livestock production has received increased scrutiny due to public health concerns over the development and dissemination antimicrobial resistance. As a result, there are efforts to replace the use of medically important antimicrobial drugs in food producing animals with novel non-antimicrobial alternatives to treat disease. One target for antimicrobial drug reduction and replacement within the beef cattle industry is the use of tylosin, a macrolide antibiotic, which is widely included within diets of feedlot cattle to reduce incidence of liver abscesses. Tylosin is considered medically important for human health, and therefore tylosin use in feedlot operations may be limited in the future. Liver abscesses are a leading cause of liver condemnation at slaughter, and result in significant financial losses to the beef cattle industry. Exposure of cattle to high concentrate diets is associated with rumen acidosis and rumenitis, leading to the formation of liver abscesses. Several non-antimicrobial strategies for the treatment of liver abscesses have been evaluated, including nutritional management, vaccines, other antimicrobial drugs, and feed additive products, although none have been shown to reduce liver abscesses as effectively as treatment with tylosin. The studies in this thesis evaluated effects of a Saccharomyces cerevisiae fermentation product (SCFP) on cattle performance, health, and microbiology outcomes. Yeast products have been shown to benefit rumen fermentation and improve cattle performance; and therefore, SCFP were hypothesized to reduce the occurrence of liver abscesses when included in diets of beef cattle raised without antibiotics. The first chapter of this thesis reviews current information about liver abscess pathogenesis, microbiology, and the use and efficacy of antimicrobial and non-antimicrobial interventions. There is a significant impact of diet, treatment, and other management factors on rumen microbial ecology, including shifts in microbiomes attached to the rumen epithelium, rumen acidosis, and microbiology of liver abscesses. The second chapter focuses on a randomized block clinical trial conducted to evaluate the effects of SCFP on animal health, growth and production, liver abscess prevalence, fecal microbiomes, and fecal resistomes in cattle raised without antibiotics using 16S rRNA gene sequencing and shotgun metagenomic sequencing. In a randomized block clinical trial, there were no statistically significant, detectable differences of SCFP supplementation on any of the tested outcomes. The third chapter characterized the liver abscess microbial community from liver abscess contents using 16S rRNA marker gene sequencing. The liver abscess microbiome was diverse and polymicrobial, and shifts in liver abscess microbiomes across cattle enrollment group demonstrates that there is a potential impact of cattle source, feedlot environment, and other factors on liver abscess microbiomes. Given the diversity of the liver abscess microbiome demonstrated in this study, more work is needed to understand the role of liver abscess microbiomes for disease severity as pre-harvest feeding strategies are investigated further in feedlot cattle.