The most widely used pasture grass in the United States may actually be harmful to livestock.

Tall fescue, found mostly in the upper South and lower Midwest, is popular for its insect and nematode resistance, tolerance of poor soil and climate conditions and long grazing season. However, it can be toxic to animals, University of Nebraska experts said.

Fescue toxicity is caused by Neotyphodium coenophialum, an internal fungus, or endophyte, that lives within plant cells of infected fescue plants. When fescue seed germinates, the endophyte can infect the plant at the base of the leaf and spreads from inside. The infection is transmitted by seed from one generation to the next, Tom Dorn, NU extension agriculturalist, said.

"The endophyte is spread only in the seed. If you planted two seeds, one endophyte infected and one not, and grew them side by side, the clump of grass resulting from the infected seed would be infected with the endophyte and the clump resulting from the non-infected seed would not be infected and would not become infected by growing next to the infected clump," Dorn said.

The endophyte produces toxic alkaloids that make the grass resistant to pests and drought and therefore seen as beneficial by homeowners. However, the endophyte is not as beneficial in pastures. Alkaloids cause problems with body temperature regulation, blood flow and feed intake in livestock. Fescue is most toxic when seed heads develop.

Problems due to fescue toxicosis can be severe.

"Typical symptoms in horses are spontaneous abortion or stillborn foals and agalactia, which is a failure to produce milk," said Jeff Pedersen, U.S. Department of Agriculture-Agriculture Research Service research geneticist at NU. "Affected cattle will have rough hair coats, will not shed hair in spring as they should, stand in water frequently to cool down and have lower rates of gain."

Fescue toxicosis in cattle also has been linked to "fescue foot," in which blood flow in extremities is restricted, causing loss of hooves, ears or tails.

"A conservative estimate places the total livestock-related losses nationwide related to tall fescue at between $500 million to $1 billion a year," Pedersen said.

Most fescue-related grazing problems occur during the summer and very cold part of winter, Bruce Anderson, NU forage specialist, said. In general, late summer and fall growth of fescue can be grazed in the latter part of the year by ruminant livestock, such as cattle and sheep, with very few problems.

Although fescue toxicosis is not a huge concern in Nebraska, abortion in horses and llamas, cases of fescue foot and poor summer performance of livestock have occurred.

Last August, Dorn worked with a Lancaster County livestock producer whose 13 female llamas had not had a live birth in three years. The herd had been feeding on fescue. Once the llamas were removed from the fescue pasture and given alternative forage, two live births were recorded after only six weeks. The females were pregnant when the change was made, but had not aborted yet, Dorn said.

"He now reports eight live births. This is from a herd that had no live births in three years," Dorn said. "Fescue had to be the problem, because that's the only thing we changed."

Though Nebraska does not have large amounts of fescue, most is infected, Anderson said. Only areas that recently have been planted with seed specifically free of endophytes are likely to be safe.

Endophyte-free fescue has been successful for general production and animal performance, but is more susceptible to insects, disease and winter injury than infected fescue.

"Because of health problems with fungus-related fescue, these shortcomings are small in comparison," said Anderson.

No consistent treatment is available for fescue toxicosis, Anderson said. However, he recommends using supplemental feed to reduce the amount of fescue livestock consume. Grazing natural range and warm-season grasses as well as adding legumes to the pasture help the animals overcome the effects of fescue toxicity and provide better nutrition, the Institute of Agriculture and Natural Resources specialist said.

Since the fungus grows within the plant and is not visible externally, laboratory analysis is required to determine if the endophyte is present.

More information about fescue toxicosis is available online at NU Cooperative Extension's Lancaster County website,

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