Endophyte Toxicity

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Knowledge Nuggets

  • Grazing grass seed fields or feeding grass seed straw from endophyte-infected forages can cause 'fescue foot' for 'fescue toxicosis'.
  • Some tall fescue and perennial ryegrass turf varieties are infected with endophytes, a fungus that lives inside of a plant (endo = inside, phyte = plant), this is a symbiotic relationship, they both benefit. The plant provides nutrients to the endophyte and the endophyte produces toxins to protect the plant from insects, diseases and grazing animals. Endophytes also help the plants tolerate drought and other environmental stresses.
  • The principal toxin that is produced is ergovaline. These toxins are vasoconstrictors, in that they constrict blood vessels and reduce the circulation to the outer parts of the animal's body. Animals that have consumed a toxic dose of ergovaline will have difficulty regulating body temperature causing 'fescue foot'. Fescue foot is characterized by gangrene or tissue death in the legs, ears and tails. Animals can become lame, and their legs can swell. Within two weeks, the tips of tails and ears or the sloughing of hooves can occur. After feeding endophyte infected forage for 10 to 20 days clinical signs of toxicity can appear.
  • Ryegrass staggers, is caused by the alkaloid lolitrem B and other lolitrem alkaloids, these toxins cause muscle tremors, muscle weakness and spasms. One may not see any clinical signs unless the animals become excited or stress, when they try to run problems arise ranging from trembling to sever in coordination to falling down. The animals would need to be fed perennial ryegrass infected with the alkaloids for 7 to 14 days to show clinical signs and these would disappear 2 to 3 days after the feed is removed but symptoms may last as long as 2 weeks.
  • The threshold levels of ergovaline that can be included in beef cattle rations is 400 to 750 part per billion (ppb) and 1800 to 2000 ppb for lolitrem B toxin. Feeds containing ergovaline or lolitrem B can be fed to animals as long as they are diluted with other feeds.
  • Endophytes are only transmitted through the seed. Its entire life cycle takes place inside the plant tissues. A stand of endophyte-infested plants cannot be "uninfected" by applying a fungicide.
  • To avoid endophyte toxins select a forage variety that is endophyte-free or low-endophyte varieties.
  • Do not feed grass seed screenings from unknown grass seed fields.
  • Ergovaline toxicity is decreased when the screenings are pelleted.
  • The endophyte fungus loses viability in the seed when stored for 18 months or more, especially if stored in hot and humid conditions. However, ergovaline can be present after several years of storage.
  • Ensiling does not decrease the ergovaline toxicity.
  • Ammoniating grass seed straw reduces the ergovaline level by about 50%.
  • Ergovaline levels can increase when the plants grow under stressful conditions.
  • Since the toxin level within endophyte-infected forage is highly variable, testing for the toxins is the best way to decide if the forage should be used for feed.
  • Oregon State University, will test forages for ergovaline and lolitrem B levels. Address: Dr. Craig's Laboratory, 139 Oak Creek Building, Endophyte Service Laboratory, College of Agricultural Sciences, Oregon State University Corvallis, OR 97331 USA Phone: 541-737-2872 Fax: 541-737-8160

Endophyte Toxins in Grass Seed Fields and Straw Effects on Livestock - available in PDF format only

Grass Seed Residues for Beef Cattle Feed

Grazing Endophyte Infected Tall Fescue

The Merck Veterinary Manual

Research Papers

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  For more information about the content of this document, contact Grant Lastiwka.
This document is maintained by Linda Hunt.
This information published to the web on November 19, 2003.
Last Reviewed/Revised on March 14, 2016.

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