URINARY AND BILIARY-EXCRETION OF ERGOT ALKALOIDS FROM STEERS THAT GRAZED ENDOPHYTE-INFECTED TALL FESCUE

Ergot alkaloids cause fescue toxicosis when livestock graze endophyte- infected (E+) tall fescue. Little is known about the bioavailability o f the ergot alkaloid classes (lysergic acid, lysergic acid amides, or ergopeptine alkaloids) in livestock, and this hampers development of p harmacological strategies to ameliorate the toxicosis. One method used to determine bioavailability of ergot alkaloids is to examine urinary and biliary excretion patterns. Thus, our objectives were to compare ergot alkaloid excretion via urinary or biliary systems and to determi ne the rate of appearance or clearance of these alkaloids in cattle th at were grazing E+ or endophyte-free (E-) tall fescue. In autumn 1996, bile and urine samples were collected from eight steers (203 kg), eac h grazing E+ and E- tall fescue, and total alkaloid excretion was quan tified using competitive ELISA. Approximately 96% of the ergot alkaloi ds were excreted in urine. The same steers were used to examine the ra te of appearance in, or clearance from, urine when switched from E+ to E-, or from E- to E+, pastures in comparison with steers that were co ntinuously grazing E+ or E- tall fescue at 0, 2, 5, and 7 d. Steers we re returned to their original pastures after 7 d, and urine was collec ted at 2, 5, and 7 d. Urinary alkaloid concentrations in steers switch ed from E- to E+ pastures were similar (P = .55) to those in steers th at continuously grazed E+ tall fescue after 2 d. Steers switched from E+ to E- pastures had urinary alkaloid concentrations similar (P = .91 ) to those in steers that continuously grazed E- pastures after 2 d. I n 1997, two trials were conducted in which steers (191 kg) were switch ed or remained on E+ or E- pastures, and urine was collected at 0, 12, 24, 48, and 96 h to estimate rate of alkaloid appearance or clearance . Steers switched from E- to E+ 1) had about 33% as much urinary alkal oids as steers grazing E+ pasture after 12 h, 2) were not different af ter 24 h(P = .76), 3) had twice those of the E+ steers at 48 h ( P < . 05), and 4) were not different after 96 h. Steers switched from E+ to E- tall fescue had approximately 33% less (P < .05) urinary alkaloids than those grazing E+ at 12 h, 67% less (P < .05) at 24 and 48 h, and were not different (P = .86) from steers continuously grazing E- pastu res after 96 h. Urinary alkaloid excretion patterns were similar to er got alkaloid solubility patterns from in vitro digestion of E+ tall fe scue. We suggest that alkaloids, liberated from the forage by ruminal microorganisms, were rapidly absorbed as lysergic acid amides and biot ransformed ergopeptine alkaloids.