Submitted to: Veterinary Medicine
Publication Type: Book / Chapter
Publication Acceptance Date: 8/17/2011
Publication Date: 2/24/2012
Citation: Aiken, G.E., Strickland, J.R. 2012. Doppler ultrasonography for evaluating vascular responses to ergopeptine alkaloids in livestock. Veterinary Medicine. In A Bird’s-Eye View of Veterinary Medicine, Edited by Carlos C. Perez-Marin. Ch 29. pp 567-586. ISBN: 978-953-51-0031-7.
Interpretive Summary: Ergot alkaloids produced by Neotyphodium fungal endophytes that infect tall and perennial ryegrassm and Claviceps fungi that infect seed heads of cereal grains can cause persistent vasoconstriction in grazing livestock that impairs their ability to dissipate body heat. This condition causes these animals to be vulnerable to severe heat streass and warm and humid environments. Color Doppler ultrasonography is a non-invasive procedure that is routinely used to assess normal and abnormal blood flow in human and veterinary medicines. It also has application as a research tool in determining vascular responses to toxicants that can effect the vasculature. These studies are ideally performed in controlled environments with animals that are at ease with human contact and do not require restraint that can cause discomfort. However, reliable measures can be collected with pastured animals with minimal human contact if control animals with no exposure to toxicants are measured for comparisons with treatment animals, and special handling procedures are employed to reduce animal nervousness and tension effects on vasculature blood flow. This book chapter discusses: 1) blood flow aspects of thermoregulation in livestock, 2) effects of ergot alkaloids on blood flow and thermoregulation and, 3) procedures and sources of error in using Doppler ultrasonography as a research tool in evaluating vasoconstrictive responses in livestock exposed to ergot alkaloids. This information will be useful in the conduct of research that is investigating vascular responses to toxicants, and further fulfills a need for rapid and non-invasive measures.
Technical 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. 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. Sheep grazing endophyte-infected fescue also can have elevated core body temperatures in warm and humid environments and reduced dry matter intake. The most pronounced effect on horses is observed with broodmares, which can exhibit prolonged gestation and agalactia. Symptomatology of the malady are reflective of alterations in hormone profil and reductions in blood flow to peripheral tissues caused by interactions of ergopeptine ergot alkaloids with biogenic amine receptors in the vasculature to induce persistent vasoconstriction and restrict regulation of core body temperature by the sympathetic nervous system. Color Doppler ultrasonography can be used as a research tool with grazing livestock to assess vasoconstrictive responses to ergot alkaloids. For optimum use of the technicology in evaluating vasoconstrictive responses in livestock exposed to ergot alkaloids, there should be a basic knowledge in blood flow aspects of thermoregulation and the effects of ergot alkaloids on blood flow and thermoregulation, and the following of imaging procedures that minimize measurement errors.