Antibiotics have been used extensively as growth promoters (AGPs) in agricultural animal production. However, the specific mechanism of action for AGPs has not yet been determined. Following early demonstrations that oral antibiotics do not have growth-promoting effects in germ-free animals, studies of the mechanism for growth promotion have focused on interactions between the antibiotics and the gut microbiota. The central hypothesis of this study is that AGPs act by influencing compositional changes to the pig gut microbiota. By changing the composition of gut microflora, AGPs improve animal health and promote growth. The overall objective of this study is to investigate alterations of the distal intestinal bacterial microflora in response to AGPs.
In this study, natural bacterial diversity of pig feces in commercial production units were described quantitatively, and changes in bacterial diversity over time were measured. Pigs receiving the AGP Tylosin were compared to pigs that did not receive Tylosin. Pyrosequencing of 16S rRNA gene libraries was used to describe the microbiota. Finally, we evaluated if the Tylosin improved swine health by reducing sub-clinical infections and inflammation, and by reducing the prevalence and load of an important zoonotic pathogen Salmonella enterica.
This longitudinal study of the microbial populations in the feces of the each pig showed that microbiome of the pig feces continued to change as pigs aged. The comparison of the microbiome between Tylosin and No-Tylosin groups showed microbial population shifts representing both microbial succession and changes in response to the use of Tylosin. Tylosin promoted the maturation of the "adult-like" fecal microbiome. However, there was no significant correlation identified between Tylosin treatment and reduce generalized inflammation. There also was no correlation between Tylosin treatments and carriage and load of Salmonella.
Overall, our results indicated that the alteration in the intestinal microflora, and its consequences, may be the underlying mechanism for beneficial effects of AGPs. Our results established a baseline upon which mechanisms of AGPs in regulation of health and growth of animals can be investigated. Furthermore, the data will aid in the identification of alternative strategies to improve animal health and consequently production.
University of Minnesota Ph.D. dissertation. June 2012. Major: Veterinary Medicine. Advisor: Dr. Richard E. Isaacson. 1 computer file (PDF); ix, 166. pages.
Kim, Hyeun Bum.
A metagenomic approach to study the effects of using tylosin an antibiotic growth promoter on the pig distal gut microflora.
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