Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Veterinary Microbiology and Preventive Medicine

First Advisor

D. L. (Hank) Harris

Second Advisor

Mark A. Rasmussen


Overfeeding ruminants with readily fermentable carbohydrates alters the normal balance of microbes in the rumen compartment causing changes in the fermentation pattern and rumen function. The resulting increase in the molar concentrations of ruminal lactate and/or volatile fatty acids (VFAs), and a decrease in ruminal pH may lead animals to experience acute or subacute acidosis. The objective of this study was to test the hypothesis that lactic acid accumulation can be inhibited by inoculating the rumen with volatile acid-producing bacteria that would compete with lactic acid-producing bacteria for substrate (starch).;We used strain 25A of Prevotella bryantii that had been selected as a rapid starch fermenter from a mixed rumen population as a rumen inoculum for in vitro or in vivo ruminal fermentations. In studies conducted in vitro; strain 25A reduced the accumulation of lactate by 90% when added to mixed rumen fermentations that contained excess soluble carbohydrates, and cultures had greater amounts of succinate and propionate compared with the controls. Morphological, biochemical and genetic analysis (sequencing of the 16S rRNA gene) indicated that strain 25A is related to Prevotella bryantii. Amylolytic strain 25A showed an ability to reduce ruminal lactate accumulation (85%) in goats in a model of acute acidosis, and was able to drive starch fermentation to VFAs and away from lactate accumulation. When the ability of this bacterium to prevent lactate accumulation was tested in lactating cows, ruminal pH was favourable (above 6) and lactate accumulation was reduced, but significant changes in ruminal VFA profile and animal milk yields were not observed.



Digital Repository @ Iowa State University,

Copyright Owner

Fernando Rodríguez



Proquest ID


File Format


File Size

114 pages