The Fescue Toxicosis Story
According to Carl Hoveland, University of Georgia, discussion of management of beef production in adverse environments cannot ignore the challenges associated with tall fescue. The cool-season perennial grass dominates more than 35 million acres grazed by approximately 13 million mother cows in the southern and southeastern United States.
Carl Hoveland, University of Georgia
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Native to Europe, tall fescue is believed to have been introduced to the United States during the nineteenth century. By 1943, it was touted as a wonder grass and recommended for seeding pastures for summer and winter grazing. Tall fescue is prolific, adapted to a wide range of soils and is resistant to drought, pests and hard grazing.
“The only thing wrong with it,” Hoveland told attendees of the 35th Annual Beef Improvement Federation (BIF) Meeting, “is cattle don’t do very well on it.”
Tall fescue’s dubious reputation stems from its association with livestock health problems resulting in poor performance. Fescue toxicosis is related to numerous alkaloids produced by a fungal endophyte that infects the plant. Hoveland said the fungus contributes to the hardiness of tall fescue. However, among cattle grazing infected fescue, endophyte-induced toxicity creates vasoconstriction with reduced blood flow to peripheral tissues.
Three separate syndromes have been associated with endophyte-infected fescue. An ailment known as fescue foot typically results in gangrene and loss of hooves, tails and ears. Bovine fat necrosis involves accumulation of hard fat along the intestinal tract, which interferes with digestion and birthing of calves. The most widespread syndrome is fescue toxicity, the symptoms of which include failure to shed winter hair, intolerance to summer heat, excessive water consumption and frequent urination. Affected cattle are prone to seek shade or to congregate in standing water.
According to Hoveland, cattle suffering from fescue toxicity generally exhibit poor gains. Low calf birth weights are common, and weaning weights may be decreased by 60-70 pounds (lb.) due to reduced milk production as well as consumption of toxic fescue by calves. Cow pregnancy rates may be reduced by 30% or more.
“Many producers simply accept a 70% calf crop, 350-pound weaning weights and stocker gains that are half of what they could be,” Hoveland stated. “But they don’t have to accept it.”
Management options for reducing the effects of fescue toxicity include pasture dilution through interseeding of additional plant species, such as legumes or other grasses, to offer diversity of diet. Grazing management can be applied to favor competitive plants present in the pasture. Providing supplemental hay or grain reduces toxicity in winter. Mowing of pastures in spring to remove seedheads will reduce toxicity since alkaloids become concentrated in fescue seed. Ammoniation of pastures also can reduce alkaloid content of infected fescue.
Hoveland said the most effective, but also the most costly solution is to destroy existing infected stands and replant with novel endophyte (non-toxic) fescue.
The BIF meeting was held May 28-31, 2003, in Lexington, Ky. To access the audio to Hoveland’s presentation or the proceedings paper, visit the newsroom.
— by Troy Smith