Tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] infected with the endophytic fungus Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin negatively affects herbivores that consume it. Horses are more sensitive to the alkaloids in endophyte infected (E+) tall fescue than cattle and exhibit increased gestation lengths, dystocia (birthing difficulty) with an increased rate of foal and mare mortality, and thickened placentas that have a tendency to separate prematurely (referred to as red-bagging), with a high rate of stillborn foals. Mares that have grazed E+ tall fescue also have poor milk production and a high rate of agalactia (lack of lactation). Sometimes, agalactic mares are aggressive toward their foals. Mares that have ingested E+ tall fescue tend to have lower IgG (immunoglobulin G) levels than normal, and it appears that their foals do not absorb the available IgGs as well as normal foals. Foals born to mares eating E+ fescue tend to be less vigorous for 2 to 3 wk post-foaling; some are not alert and exhibit a nonresponsive type of behavior. Growth rate of such yearlings is lower than normal unless they receive supplemental feed. Preliminary research data suggest that mares on E+ fescue have prolonged luteal (corpus luteum, located on the ovary) function, decreased per cycle pregnancy rates, and increased early embryonic death rates. Oral administration of domperidone 10 to 20 d before expected foaling effectively prevents the signs of fescue toxicosis in gravid mares. Domperidone administered to 1423 mares in the United States under veterinarian supervision and under field conditions was 95% effective in preventing signs of tall fescue toxicosis.

Keywords: tall fescue, endophyte, domperidone, dystocia, agalactia, prolactin, placenta, ergot alkaloids.

Abbreviations: ACTH, adrenocorticotrophic hormone; CRH, corticotrophic releasing hormone; E-, endophyte free, free of Neotyphodium; E+, infected by wild Neotyphodium endophyte; HPA, hypothalamic-pituitary-adrenal axis; IgG, immunoglobulin G; NRC, National Research Council; PRL, prolactin; TSH, thyroid stimulating hormone.


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Table of Contents

Tall Fescue Monograph

See Related Information In:

Chapter 2: Evolutionary Origins and Geographic Distribution of Species in Subgenus Schedonorus

Chapter 3: Summer Survival

Chapter 5: Switching From E+ To E- Stands

Chapter 11: Introduction 

Chapter 12: Toxicokinetics of the Ergot Alkaloids 

Chapter 13: Introduction 

Chapter 16: Treating Animals