Tips for avoiding tall fescue toxicosis

Grazing specialists at the Iowa Beef Center, Ames, Iowa, recommend that producers check their pastures for tall fescue. Widely used for forage, turf, road ditches and conservation acres, tall fescue is a cool-season grass found throughout the Midwest. Some producers purposely choose tall fescue for their pastures while others unknowingly plant the grass as a component in pre-packaged 'pasture mixtures' or while seeding CRP acres.

"Tall fescue has many of the traits producers want in a pasture grass," says Steve Barnhart, Iowa State University Extension forage specialist and a professor in the Agronomy Department. "Tall fescue is a winter hardy, cool-season grass that is productive from April through October. It is compatible in mixtures with other forage grasses and legumes, and can be used for hay or pasture. It can produce a traffic-tolerant sod, and stands up well to intensive or even abusive grazing. "However, a fungus associated with much of Iowa's tall fescue can be a problem in livestock production programs," he adds.

Much of tall fescue in the Midwest harbors a fungus that resides in the grass plant as an endophyte. The fungus doesn't negatively affect the grass plant; it actually adds some disease and stress resistance to the fescue plant, contributing to its competitiveness.

"The fescue plants with the endophyte fungus contain chemical constituents called alkaloids that can lead to a number of physiological and production problems for livestock that eat them," Barnhart says. "The alkaloids cause blood vessel constriction in grazing animals, and leads to a long list of associated ailments called fescue toxicosis syndrome."

In hot weather, large animals can overheat, adversely affecting daily forage intake, rates of gain, milk yield and reproduction. Symptoms include rough hair coats, limited mid-day grazing and frequent standing in streams or ponds. In cold weather, poor circulation can cause lost ear tips, tails, lameness, and in extreme situations, hooves.

Horses can suffer extended gestation, retained placentas, reduced milk production and even abortions when grazing endophyte-infected fescue pastures and eating endophyte-infected fescue hay.

"Tall fescue plants can be identified by closely inspecting the pasture," Barnhart explains. "They're found as distinct clumps or bunches in the sod. The green, leafy grass blades are stiff and often darker green than surrounding grasses. The upper surfaces of the leaf blades have deep grooves from base to tip, the bottom surface is smooth and shiny. The edges of the leaf blades are serrated – finely saw-toothed from tip to base."

"Many producers successfully manage pastures containing fescue, using some general 'good management' practices," Barnhart says. "Producers can begin monitoring pastures now so they can start management as soon as fescue is identified.

"Seed stems, seed heads and lower stem bases contain the highest concentrations of alkaloids; the green leaf blades the least," Barnhart says. Management that minimizes animal access to seed stems and maximizes the grazing of leaf blades goes a long way to lessening the undesirable affects of fescue in pastures.

Management for stands with 50 percent or less tall fescue should start with clipping seed stems in May and June to keeping it in the leafy, vegetative condition. Seedheads generally do not develop for the remainder of the year. Avoid high or excessive nitrogen and manure applications. In addition, consider adding legumes such as clovers, birdsfoot trefoil or alfalfa to contribute toward a dilution of the fescue consumption. Dividing the pasture into smaller areas and rotational grazing also is a helpful practice.

Management of stands with 50 to 75 percent fescue should include clipping seedheads, minimizing nitrogen applications and incorporating legumes. Rotational grazing also would be an applicable procedure. At this level of tall fescue composition, producers should consider sampling and testing fescue plants to determine the level of endophyte infection in the stand, which would enable them to make better short- and long-term fescue management plans.

At greater than 75 percent fescue population and/or where endophyte infection is known to exist and animal production is being affected, producers should begin to plan for destruction of the old stand and a complete renovation of the pasture. Contact ISU Extension livestock or crop production specialist when planning a fescue pasture renovation. For help identifying tall fescue, producers can find close-up pictures on the Iowa Beef Center Web site at


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