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FORAGE & GRAZINGLANDS

Ruminal Metabolism and Transport of Tall Fescue Ergot Alkaloids

^a Dep. Crop and Soil Sciences, Univ. of Georgia, Athens, GA 30602
^b College of Veterinary Medicine, Univ. of Georgia, Athens, GA 30602
^c Veterinary Medical Diagnostic Lab., Univ. of Missouri, Columbia, MO 65211
^d USDA-ARS J. Phil Campbell Sr. Natural Resource Conservation Center, Watkinsville, GA 30677. This research was funded by the Animal Health and Well Being Program Area of the United States Department of Agriculture Competitive Grants Program under Agreement No. 2001-35204-09958. All research was conducted in accordance with the UGA Animal Care and Use Committee approval no. A2001-10217-0

^* Corresponding author (nhill{at}uga.edu).

Circumstantial evidence suggests ergovaline is the putative toxin causing fescue toxicosis. However, several investigators suggest lysergic acid may be involved as well. Therefore, the purpose of this study was to (i) determine the metabolic fate of ergot alkaloids in ruminants, (ii) investigate gastric transport, and (iii) validate these findings in vivo. Ruminal metabolism of the alkaloids was determined by inoculating endophyte-infected and endophyte-free tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] with viable and nonviable ruminal fluid using in vitro techniques. Total ergot alkaloid concentration increased with time due to microbial metabolism. The alkaloids were extracted, and ruminal and omasal transport investigated in vitro. Only lysergic acid crossed gastric barriers. To validate the findings, fistulated steers were allowed to graze endophyte-infected or endophyte-free tall fescue paddocks in a crossover study, and ruminal fluid and urine were analyzed for ergot alkaloids over time. Ergovaline was not found in ruminal fluid or urine. Urine was immunopurified from a steer grazing endophyte-infected tall fescue and analyzed by high-performance liquid chromatography. A peak with a signal consistent with lysergic acid was found. These results imply that lysergic acid may be involved in the fescue toxicosis syndrome.

Abbreviations: ELISA, enzyme-linked immunosorbent assay • HPLC, high-performance liquid chromatography • KRPG, Krebs–Ringer phosphate solution with 10 mM glucose