Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/1998
Publication Date: N/A
Citation: N/A Interpretive Summary: Tall fescue occupies approximately 35 million acres of land in the United States. Most is infected with a fungus that positively influences productivity and survival of the plant, but negatively influences livestock performance and productivity by an estimated 0.5 to 1.0 billion dollars annually. Ergot alkaloids are generally accepted as the primary factor responsible for the reduced livestock performance and production known as fescue toxicosis. It has been difficult to develop methods to overcome the toxicosis because there is no information on the bioavailability of the various alkaloids in livestock. One method used to determine bioavailability is to examine alkaloid excretion patterns. Our research found that 20 times more alkaloid was being excreted via the urine than the bile. Examination of the urinary alkaloid excretion patterns revealed that it was a very sensitive measure of consumption of toxic fescue. It further indicated that the alkaloids were absorbed very rapidly following consumption, and that pharmacologic strategies to overcome toxicosis may be developed to block absorption as a pre-emptive measure rather than blocking their metabolic effect once in the circulatory system.
Technical Abstract: The objectives of this research were to compare ergot alkaloid excretion via urinary or biliary systems and to determine the rate of appearance or clearance of these alkaloids in cattle grazing endophyte-infected (E+) or endophyte-free (E-) tall fescue. Bile and urine samples were collected from eight steers grazing E+ and E- tall fescue and total alkaloid excretion quantified using competitive ELISA. Approximately 96% of ergot alkaloid excretion was in the urine. Urinary alkaloid concentrations in steers switched from E- to E+ pastures were similar (P=0.55) to steers that continuously grazed E+ tall fescue after 2 d. Likewise, after 2 d, steers switched from E+ to E- pastures had similar (P=0.91) urinary alkaloid concentrations as steers that continuously grazed E- pastures. In two subsequent trials with different steers, when comparing steers switched from E- to E+ pastures and those continuously grazing E+ tall fescue, at 24 h there were no differences (p=0.76), at 48 h, switched steers had twice that of the E+ steers (P<0.05), and no differences at 96 h (P=0.81). Steers switched from E+ to E- tall fescue had approximately 33% less (P<0.05) urinary alkaloids at 12 h, 67 % less (P<0.05) at 24 and 48 h, and were not different (P=0.86) from steers continuously grazing E- pastures after 96 h. These data indicate that alkaloids are rapidly absorbed as lysergic acid amides and biotransformed ergopeptine alkaloids.