Doppler Ultrasonography for Evaluating Vascular Responses to Ergopeptine Alkaloids in Livestock

Abstract

Ergot alkaloids are produced by non-spore producing fungal endophytes that infect certain species of grasses, most notably tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] and perennial ryegrass (Lolium perenne L.), and the spore producing Claviceps spp. that infect seed heads of certain grasses and particularly the cereal grains [rye (Secale cereal L.), barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), , and oats (Avena sativa L.)] (Strickland et al., 2011). Ergot alkaloids induce a toxicosis in grazing livestock, with symptoms in cattle that include rough hair coats during the warm season, severe heat stress in warm and humid temperatures, reduced dry matter intake, agalactia, and poor reproductive and weight gain performance (Porter & Thompson, 1992; Paterson et al., 1995). Sheep grazing endophyte-infected fescue also can have elevated core body temperatures in warm and humid environments (Zanzalari et al., 1989; Hanna et al., 1990), and reduced dry matter intakes (Chestnut et al., 1992; Aldrich et al., 1993). The most pronounced effect on horses is observed with broodmares, which can exhibit prolonged gestation and agalactia (Cross et al., 1995). Symptomatology of the malady are reflective of alterations in hormone profiles (Porter & Thomson, 1992; Browning et al., 1997, 1998) and reductions in blood flow to peripheral tissues caused by interactions of ergopeptine ergot alkaloids with biogenic amine receptors in the vasculature (Oliver et al., 1998) to induce persistent vasoconstriction and restrict regulation of core body temperature by the sympathetic nervous system (Oliver, 1997). Consequently, lack of thermoregulation by livestock exposed to ergopeptines are extremely vulnerable to heat and cold stresses (Hemken et al., 1981; Al-Haidary et al., 2001).