Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation




Animal and Food Sciences

First Advisor

Dr. David L. Harmon


Ergot alkaloids present in endophyte-infected (E+) tall fescue are thought to be the causative agent of fescue toxicosis, a syndrome affecting cattle in the eastern United States. Many of the observed signs of fescue toxicosis are thought to be attributed to peripheral vasoconstriction; however, there are data indicating that ergot alkaloids can alter blood flow to the gut. An experiment was conducted using right ruminal artery and vein collected from heifers shortly after slaughter. Vessels were mounted in a multi-myograph to determine the vasoconstrictive potentials of ergot alkaloids present in E+ tall fescue. Results indicated ergot alkaloids have the potential to induce vasoconstriction of foregut vasculature. A second experiment was conducted to determine if the additional ergot alkaloids present in E+ tall fescue increase the vasoconstrictive response above that of ergovaline. Results indicated that ergovaline is the main alkaloid responsible for vasoconstriction in bovine vessels. A third study was performed to determine the effect of ergot alkaloids on ruminal epithelial blood flow in the washed rumen of steers exposed to E+ or endophyte-free (E-) tall fescue seed. Steers were dosed with seed followed by a washed rumen experiment with differing levels of ergovaline incubated in the rumen. Results indicated that E+ tall fescue seed treatment reduced ruminal epithelial blood flow. Additionally, incubating ergovaline in the rumen during the washed rumen further decreased epithelial blood flow and volatile fatty acid (VFA) absorption. A final study was conducted to determine the acute effects of ergot alkaloids on isolated rumen epithelial absorptive and barrier functions and the potential for ruminal ergovaline absorption. Results indicate that acute exposure to ergot alkaloids does not alter the absorptive or barrier function of rumen epithelium and ergovaline is absorbed from the rumen. Data from this series of experiments have shown that ergot alkaloids from E+ tall fescue can induce vasoconstriction of blood vessels in the foregut of cattle, reduce blood flow to the rumen epithelium, and decrease VFA absorption. The decrease in nutrient absorption could contribute to the observed symptoms of fescue toxicosis, including depressed growth rates and general unthriftiness.