Tall fescue [Lolium arundinaceum (Schreb.) Darbysh., previously known scientifically as Schedonorus arundinaceus (Schreb.) Dumort.] is a cool-season, perennial grass (Figure 1). The Continental type, most notably the Kentucky-31 variety, is frequently infected with an endophyte (Epichloë coenophiala). An endophyte is a fungus that grows inside the grass, specifically within the intercellular spaces of the leaf sheaths, stems, and seeds, and is invisible to the naked eye. The plant and fungus have a mutually beneficial relationship, wherein the plant provides the fungus access to its nutrients and a means of asexual reproduction through infected seeds. In turn, the fungus produces compounds called ergopeptine alkaloids that increase the plant’s vigor by making the plant more pest- and drought-resistant and more tolerant of other adverse soil and environmental conditions. Although advantageous to the plant, ergopeptine alkaloids adversely affect the health and productivity of grazing livestock. Ergovaline is the most abundant (more than 90 percent) and most toxic ergopeptine alkaloid in endophyte-infected (E+) tall fescue. The highest alkaloid concentrations are found within the seedheads and in the bottom few inches of the plant.