Submitted by Christopher Petty, Southwind Extension Agent
According to the University of Tennessee Agricultural Extension Service, in the late 1970s, it was discovered that the poor performance and toxicosis symptoms were associated with cattle grazing tall fescue infected with the fungus Neotyphodium coenophialum. The terms “fescue fungus,” “endophyte,” “fungal endophyte” and “fescue endophyte” have all been used to describe this fungus.
“Endo” (within) plus “phyte” (plant) means a plant living within another plant. This fungus lives and grows between the cells of a tall fescue plant, and produces no signs or symptoms on the plant. Effects of the endophyte on grazing cattle can be seen as one or more of several clinical signs, including: lower feed intake, lower weight gains and rough hair coats during the summer, lower milk production, reduced reproductive performance, more time spent in shade and water and necrosis of hooves, tail, etc., commonly referred to as “fescue foot.”
An adapted strain of this grass was discovered growing on a farm in Kentucky in 1931. The cultivar “Kentucky-31” was released in the early 1940s, and was widely accepted by farmers throughout the Southeast because of its wide range of adaptation, ease of establishment and persistence. It gained a reputation as a low palatability forage that resulted in poor animal gains and various toxicosis symptoms, even though chemical analysis indicated that tall fescue was as good as any other cool-season grass. It was noted that dry matter intake was less in animals grazing tall fescue compared to those grazing other grasses. Early explanations for the poor palatability and intake were the coarse leaves and stems, and sharp edges on leaves.
In beef cattle, the term “summer slump” has been used to refer to fescue toxicosis, because of the visual symptoms that occur during most summers (e.g. Rough hair coat, extended time in shade and water). Because of this, many people assume that fescue toxicosis is primarily a summer problem. Research has shown that animal performance is reduced throughout the year, with the largest decreases in weight gains occurring during spring rather than summer.
Even though the presence of the endophyte in tall fescue results in toxicity symptoms, there are some positive aspects to endophyte infection. Research and practical experience have shown that endophyte infected tall fescue is more persistent than endophyte-free fescue in pasture. This difference became noticeable as the first endophyte-free varieties were used. Stands of endophyte-infected tall fescue had been grazed for many years and were still solid. The new stands of endophyte-free tall fescue became weedy and were often lost after only a few years. Novel “friendly” endophyte varieties are now available, with less negative consequences for cattle, but still retaining some positive benefits to the fescue.
The greater persistence of infected tall fescue is due to its enhanced ability to tolerate stress. The endophyte increases the tolerance of tall fescue to drought, disease, insects, grazing pressure or combinations of these, resulting in a more persistent plant.
Because of this, all producers with tall fescue pastures should ask themselves two questions: Are my tall fescue pastures infested with the endophyte and if my pastures are infested? What should I do about it? To find answers to these questions contact your local extension office.