Effect of acute exposure to ergot alkaloids on short-chain fatty acid absorption and barrier function of isolated bovine ruminal epithelium

Abstract Text:

Ergot alkaloids present in endophyte-infected tall fescue are the causative agents for fescue toxicosis in cattle. Ergot alkaloids have been shown to cause a reduction in blood flow to the rumen epithelium as well as a decrease in short-chain fatty acid (SCFA) absorption from the washed rumen of steers. It is possible that ergot alkaloids could negatively impact SCFA transport pathways and the barrier function of the rumen epithelium. An experiment was conducted to determine if acute exposure to an endophyte-infected tall fescue seed extract (EXT) would affect total, passive, or facilitated acetate and butyrate flux across the isolated bovine rumen epithelium as well as the barrier function measured by inulin flux and tissue conductance (G_t). Flux of ergovaline across the ruminal epithelium was also evaluated. Ruminal 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 under voltage clamp conditions. In vitro treatments included vehicle control (0.4% methanol), Low EXT (50 ng ergovaline/mL), and High EXT (250 ng ergovaline/mL). Results indicate that there was no effect of an 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 G_t (P > 0.17) also were not affected by EXT treatment, indicating no alteration in barrier function due to acute ergot alkaloid exposure. Based on ergovaline concentrations measured in the serosal buffer of the High EXT treatment, the flux rate is approximately 0.25 – 0.44 ng/(cm² · h). These data indicate that specific pathways for SCFA absorption and barrier function of the ruminal epithelium are not affected by acute exposure to an extract of tall fescue seed at the concentrations tested. Ergovaline has the potential to cross the rumen epithelium of cattle which could contribute to the reduced foregut blood flow seen in previous experiments and lead to reduced growth rates of cattle. 

Keywords: Ergot Alkaloids, Ergovaline Absorption, Fescue Toxicosis