By Brad Johnson
It’s not a huge secret that Tall Fescue (Festuca arundinacea) is the dominant pasture forage species throughout the lower Midwest and Southeast. Tall Fescue is well known for being very hardy, insect and nematode resistant, plus tolerating poor management, soil and climatic conditions.
What seems to not be well known about Tall Fescue is that much of it is infected with a fungal endophyte (Neotyphodium coenophialum).
Let’s review some history first. According to Dr. Craig Roberts, Department of Agronomy at the University of Missouri, Tall Fescue was brought to the United States from Europe in the late 1800s. It was officially discovered in Kentucky in 1931, tested at the University of Kentucky, and was released to the public in 1943 as the well known “Kentucky 31” variety. It is estimated that Tall Fescue now covers over 40 million acres of pasture and forage land in the U.S.
According to Dr. Peter Cheeke, Oregon State University, livestock producers soon discovered that the performance of their animals grazing Tall Fescue was poor. Cattle often grew poorly and developed a chronic, unthrifty condition, especially in the summer. This came to be referred to as “Summer Fescue Toxicosis” or “Summer Slump.” In addition, cattle grazing fescue pastures during the winter sometimes developed lameness and gangrene of the extremities (hooves, tail, ear-tips). This condition is called “Fescue Foot.”
In the 1970s, USDA and university researchers identified that in certain pastures no fescue toxicosis occurred, while in adjacent pastures, the livestock displayed toxicity symptoms. Comparison of the grasses from each pasture led to the determination that Tall Fescue causing toxicity symptoms was infected with an endophyte (“in plant”) or fungi that live entirely within the tissue spaces of the plant. This endophyte produces toxic ergot alkaloids, which cause summer fescue toxicosis and fescue foot. Endophyte-free Tall Fescue is non-toxic.
The endophyte has a mutualistic relationship with the grass. The plant provides the fungus with a nutrient-rich protected environment and a means of reproduction, while the fungus produces chemicals that serve as a defense mechanism for the grass. Compared to endophyte-free Tall Fescue, toxic endophyte infected Tall Fescue is more vigorous, pest and drought-resistant, and tolerant of poor management.
Horses are the only livestock whose reactions to toxic endophyte infected Tall Fescue are almost exclusively related to poor reproduction. Pregnant mares grazing toxic endophyte infected Tall Fescue may experience prolonged gestation, difficulty foaling, lack of milk production, thickened placenta, and large weak foals with elongated hooves. Tall Fescue effects are expressed when mares are consuming toxic endophyte infected Tall Fescue from day 300 of pregnancy through foaling. Mares not fed toxic endophyte infected Tall Fescue from day 300 of pregnancy through foaling result in normal foaling. Several other solutions exist for pregnant mares that have been fed toxic endophyte infected Tall Fescue and it is strongly suggested that a veterinarian be consulted very early in a mare’s pregnancy.
Cattle grazing toxic endophyte infected Tall Fescue for several years have been found to have necrotic fat lesions throughout their abdominal cavity. Fat necrosis seems to be associated with Tall Fescue that has been heavily fertilized with nitrogen or poultry litter.
The symptoms caused by toxic endophyte infected Tall Fescue in all livestock species result from the ergot alkaloids causing blood vessels to constrict (vasoconstrictor).
The most obvious way to prevent fescue toxicity problems is to avoid exposure of livestock to toxic endophyte infected Tall Fescue. But, that’s not realistic. Practical conditions in the Southeastern U.S. dictate that the major forage grass grown will be endophyte-infected Tall Fescue. Tall Fescue seeds are highest in ergot alkaloid content. Thus avoid grazing during this maturity stage and mow pastures to prevent seedhead formation. Legumes (clover, vetch, lespedeza, etc.) and other cool season grasses (orchardgrass, brome, matua, etc.) can be interseeded into toxic endophyte infected Tall Fescue or added to a seed mixture, to dilute the effects. Non-toxic endophyte infected Tall Fescue varieties (known as endophyte neutral or endophyte friendly) have been developed. These varieties contain the endophyte, which imparts the hardiness and insect resistance, but do not produce the toxic ergot alkaloid.
Testing for the toxic endophyte can be done at the NCDA&CS forage testing lab in Raleigh. The Rowan County Cooperative Extension Office, 2727-A Old Concord Road, has information, instructions, and paperwork for those interested.
Agriculture-Livestock and Dairy
Rowan County Cooperative Extension