Location: Forage-animal Production ResearchTitle: Acute exposure to ergot alkaloids from endophyte-infected tall fescue does not alter absorptive or barrier function of the isolated ruminal epithelium Author
Submitted to: Animal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2014
Publication Date: 6/1/2014
Citation: Foote, A.P., Penner, G.P., Walpole, M.E., Klotz, J.L., Brown, K.R., Bush, L.P., Harmon, D.L. 2014. Acute exposure to ergot alkaloids from endophyte-infected tall fescue does not alter absorptive or barrier function of the isolated ruminal epithelium. Animal. 8(7):1106-1112. Interpretive Summary: Ergot alkaloids such as ergovaline are synthesized by the endophyte (Neotyphodium coenophialum) present in tall fescue (Lolium arundinaceum) and are thought to be the main causative agents of fescue toxicosis in beef cattle. Consumption of endophyte-infected tall fescue has been shown to reduce blood flow to the gut of cattle. Endophyte-infected tall fescue seed extract has been reported to cause constriction of the ruminal artery and veins and a large reduction in epithelial blood flow to the washed reticulorumen of steers. Along with the reduced epithelial blood flow, a marked reduction in VFA flux across the washed rumen has been reported. Additionally, a greater quantity of propionate, butyrate, and valerate were absorbed across the washed reticulo-rumen wall per unit of blood flowing to the reticulo-rumen epithelium. This indicates that ergot alkaloids may have a direct effect on the rumen epithelial cells that causes an increase in VFA absorption per unit of blood flow. The objectives of this experiment were to 1) determine the effect of acute exposure to ergot alkaloids on total, facilitated, and passive VFA flux across the isolated bovine rumen epithelium, 2) determine the effect of acute ergot alkaloid exposure on isolated rumen epithelial barrier function, and 3) determine the flux of ergovaline, a principal alkaloid present in the tall fescue seed extract, across the rumen epithelium. Results from this experiment show that ergot alkaloids present in endophyte-infected tall fescue do not have an impact on nutrient absorption or barrier function of the isolated rumen epithelium of cattle following acute exposure indicating the previously observed reduction in nutrient absorption in live animals exposed to ergot alkaloids requires chronic exposure or is driven by the reduced blood flow. Results also show that ergovaline, one of the main causative agents of fescue toxicosis, is absorbed across the rumen epithelium, although it is at a fairly slow rate approximating 1% of a daily dose. This is the first known report to show that ergovaline crosses the bovine rumen epithelium.
Technical Abstract: Ergot alkaloids in endophyte-infected (Neotyphodium coenophialum) tall fescue (Lolium arundinaceum) have been shown to cause a reduction in blood flow to the rumen epithelium as well as a decrease in VFA absorption from the washed rumen of steers. Previous data also indicates that incubating an extract of endophyte-infected tall fescue seed causes an increase in the amount of VFA absorbed per unit of blood flow, which could result from an alteration in the absorptive or barrier function of the rumen epithelium. An experiment was conducted to determine if an endophyte-infected tall fescue seed extract (EXT) would affect total, passive, or facilitated acetate and butyrate flux across the isolated bovine rumen as well as the barrier function measured by inulin flux and tissue conductance (Gt). Flux of ergovaline across the rumen epithelium was also evaluated. Rumen tissue from the caudal dorsal sac of Holstein steers (n = 6), fed a common diet, was collected and isolated shortly after slaughter and mounted between two halves of Ussing chambers. In vitro treatments included vehicle control (80% methanol; 0.5% of total volume), Low EXT (50 ng ergovaline/mL), and High EXT (250 ng ergovaline/mL). Results indicate that there is no effect of acute exposure to ergot alkaloids on total, passive, or facilitated flux of acetate or butyrate across the isolate bovine rumen epithelium (P > 0.51). Inulin flux (P = 0.16) and Gt (P > 0.17) were not affected by EXT treatment, indicating no alteration in barrier function due to acute ergot alkaloid exposure. Ergovaline was detected in the serosal buffer of the High EXT treatment indicating that the flux rate is approximately 0.25 – 0.44 ng/(cm2 • h). Data indicates that specific pathways for VFA absorption and barrier function of the rumen epithelium are not affected by acute exposure to ergot alkaloids from tall fescue at the concentrations tested. Ergovaline has the potential to be absorbed from the rumen of cattle which could contribute to reduced blood flow and motility and lead to reduced growth rates of cattle.