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TALL FESCUE TOXICOSIS
By: "Craig Roberts, Dept. of Agronomy, Univ. of MO."
Tall fescue (Festuca arundinacea) is Missouri's most widely used forage crop. It is insect and nematode resistant, tolerates poor soil and climatic conditions well and has a long growing season. Unfortunately, tall fescue also has a downside. Most tall fescue in the state is infected with a fungal endophyte, Neotyphodium coenophialum (formerly called Acremonium coenophialum) that is toxic to animals.
Tall fescue was brought to this country from Europe in the late 1800s. It was officially discovered in Kentucky in 1931, tested at the University of Kentucky and released in 1943 as "Kentucky 31." It became popular with farmers in the mid- to late-1940s and 1950s, spreading quickly throughout the midwestern and southern United States. Today it is accounts for well over 40 million acres of pasture and forage land in this country. In Missouri alone, tall fescue covers approximately 17 million acres.
Early producers of tall fescue were excited by the ease with which they could establish and maintain a stand. Soon, however, conflicting reports began circulating. For some reason animals were not performing well when allowed to graze tall fescue. Research into the causes of poor animal performance resulted in the discovery of a small fungus that grows between the cells. This fungus came to be known as the "endophyte" because it was "in" (endo) the "plant" (phyte). Follow-up research revealed that this endophyte could produce ergot-like alkaloids under certain conditions.
How does the endophyte affect grazing animals?
How does the endophyte affect different animal species?
Research from across the southern United States shows that the endophyte can reduce weight gain by more than 50 percent in steers fed on pasture (see Table 1). It also shows that the seed head is the most toxic portion of the plant.
Agalactia — a diminished ability to produce milk — is especially severe when cows graze tall fescue during the last trimester of gestation. Agalactia leads to thickened placentas, aborted fetuses and, if the offspring should survive, a lack of colostrum and milk for the calf.
Tall fescue fertilized with high levels of nitrogen can also lead to bovine fat necrosis. As hard masses appear in the fatty tissues surrounding the intestines, this condition causes digestive problems and can also interfere with calving. High nitrogen rates also increase concentrations of toxic alkaloids such as ergovaline.
Table 1. Effect of the endophyte on weight gain in steers.
Foals that survive in utero will generally be larger than normal, have overgrown hooves, poor suckling reflexes, incoordination and lowered body temperatures. Foals may also have poor immunity due to the lack of colostrum produced by the mare. Because horses are sensitive to the toxins in endophyte-infected tall fescue, even the lowest levels of endophyte can produce equine fescue toxicosis.
Life cycle of the endophyte
It is important to understand how the endophyte spreads — from inside the plant (Figure 1). In its natural setting, it does not form spores and infect other plants from the air. Thus, a well-established field of endophyte-free tall fescue will not become reinfected unless the stand thins, thereby creating an opportunity for infected seed to germinate and become established.
Figure 1. The tall fescue endophyte fungus inside a leaf sheath cell. The fungus is not found in a leaf blade.
How to determine the presence of endophyte-infected tall fescue
Is the endophyte present?
Alternative tall fescue cultivars are those infected with the "novel" endophytes. These cultivars are currently being released as a compromise between infected and endophyte-free cultivars. The novel endophytes are special strains of fungus that contain much less toxin than the old endophyte. They are inserted into the plant to increase persistence.
In making management decisions, producers should consider the suggestions listed below The first suggestion is to replace infected Kentucky 31 tall fescue with endophyte-free tall fescue or another forage. The other suggestions are based on managing infected fescue.
Caution must be exercised in the process of renovation. If the land is drought-susceptible or heavily grazed, total renovation is not wise. It is more prudent to renovate a small portion of the farm. If the land is productive, larger renovations are appropriate. In three independent studies conducted in the midwestern and southern United States, replacement with endophyte-free fescue has been cost-effective.
In summary, although tall fescue is a viable and important forage for grazing animals, not all tall fescue cultivars are alike. Each must be managed with an understanding of the endophyte status. Those fields infected with a toxic endophyte will require management of the animal for weight gain, reproduction, and milk production. Those cultivars that are endophyte-free will require a similar level of management, though most of the effort will be directed toward plant persistence. New cultivars infected with "novel" endophytes may offer improved animal performance and plant persistence.
About the author: Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. Ronald J. Turner, Director, Cooperative Extension Service, University of Missouri and Lincoln University, Columbia, Missouri 65211. • University Extension does not discriminate on the basis of race, color, national origin, sex, religion, age, disability or status as a Vietnam era veteran in employment or programs. If you have special needs as addressed by the Americans with Disabilities Act and need this publication in an alternative format, write ADA Officer, Extension and Agricultural Information, 1-98 Agriculture Building, Columbia, MO 65211, or call (573) 882-8237. Reasonable efforts will be made to accommodate your special needs.
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