Study shows danger of short grazing toxic fescue pastures by cattle herds

New findings will be great help in pasture grazing management.

New forage research gives reason to not graze toxic fescue grass too short, as the bottom 2 in. of infected grass were found to hold highest levels of the alkaloid that cause problems for grazing livestock.

The findings guide ways to manage fescue’s toxic impact, according to Craig Roberts, University of Missouri Extension forage specialist.

The message for cattle herd owners: Don’t allow cows to grub fescue pastures into the ground.

Sarah Kenyon reported her study findings in a doctoral dissertation accepted at the University of Missouri this year. The results will be published in Crop Science, a scientific journal.

Kenyon, an University of Missouri Extension agronomist at West Plains, Mo., took grass samples twice per growing season for three years. The first was in April prior to boot stage (seed set) and the second in October prior to frost. Previous research showed that the plants are most toxic after seed set. She found that the most toxic portion is the bottom 2 in. At seed set, the plant is also toxic -- just not as toxic or edible.

These findings are new, Roberts said, and will be a great help in pasture grazing management.

For her study, Kenyon tested fescue owned by Tom Roberts, a cow/calf producer in Alton, Mo., that is grazed and cut for hay. In the studies, Kenyon cut fescue tillers into 2 in. segments from root crown to top. Each layer was analyzed separately by Nick Hill of Agrinostics lab in Watkinsville, Ga.

Over the years, farmers have developed ways to prevent toxic fescue poisoning. They learned that seed heads and stems were high in toxin. Grazing before seed set or clipping heads reduced toxicosis.

Now, farmers will know not to graze down to the root crown, Kenyon said. Leaving a 3 in. stubble reduces problems.

“This research can be used immediately by Missouri farmers,” Craig Roberts said. “It will be taught at (University of Missouri) grazing schools.”

The toxic alkaloid, an ergovaline, is found in Kentucky 31 fescue, the most-used grass in Missouri pastures. For years, farmers knew of problems caused by toxicosis. The most serious symptom shows up in winter as fescue foot. The toxin constricts blood flow to cattle extremities. Ears, tails and feet can freeze. Tails can fall off.

The toxin comes from an endophyte fungus inside the plant. Endophyte means “inside the plant,” and it took years for scientists to find the tiny fungus growing between plant cells.

Fescue foot often causes lost hooves. That prevents cows from walking and grazing, and results are fatal. Other losses can be serious but obscure. Cows abort or fail to breed, which reduces the calf crop. Calves raised on fescue gain slowly. Mother cows grazing toxic fescue produce less milk.

Another symptom is brown hair that won’t shed in summer. Cattle suffering heat stress will stand in ponds to cool off rather than graze.

In horses, the toxin causes foal death at birth.

The best way to solve toxicosis is to kill the toxic grass and reseed a novel-endophyte fescue. Plant breeders introduced a naturally occurring nontoxic fungus into new varieties. Novel endophytes protect the plants but aren’t toxic.

Nick Hill at Agrinostics leads quality control tests for the Alliance for Grassland Renewal. The alliance teaches farmers the danger of fescue and how to plant new novel-endophyte varieties.

In the past five years, the alliance held workshops in Missouri, but now it is adding other states in the fescue belt, which covers the southeastern quarter of the U.S. This year, alliance workshops are set for March in five states: Missouri, Kentucky, Virginia, North Carolina and South Carolina. See information on the education page of the alliance website at www.grasslandrenewal.org.

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